By Nick Macfie

ISLAMABAD (Reuters) - China and Pakistan should make cooperation on power generation a priority, Chinese Premier Li Keqiang said, as Islamabad seeks to end an energy crisis that triggers power cuts of up to 20 hours a day, bringing the economy to a near standstill.

Li arrived in the Pakistan capital on Wednesday on the second leg of his first official trip since taking office in March after a visit to Pakistan's and China's arch rival, India.

Tight security included shutting down mobile phone networks across the city.

Pakistan was one of the first countries to switch diplomatic allegiance from Taiwan to China, in 1950, and they consider each other "all-weather friends".

In an interview with Pakistan media, Li said there was still "great potential" for the relationship. Bilateral trade last year rose above $12 billion for the first time and both sides are aiming to reach $15 billion in the next two or three years.

"Our two sides should focus on carrying out priority projects in connectivity, energy development and power generation and promoting the building of a China-Pakistan economic corridor," Li said.

The power shortages have sparked violent protests and crippled key industries, costing hundreds of thousands of jobs in a country already beset by high unemployment, a failing economy, widespread poverty, sectarian bloodshed and a Taliban insurgency.

There are several joint energy and infrastructure projects under way in Pakistan and China has taken over operation of the strategically important Gwadar port.

When complete, the port, which is close to the Strait of Hormuz, a key oil shipping lane, is seen opening up an energy and trade corridor from the Gulf, across Pakistan to western China, and could be used by the Chinese Navy, upsetting India.

Li this week offered India a "handshake across the Himalayas" and said the world's two most populous nations could become a new engine for the global economy - if they could avoid friction.

China and India disagree about large areas of their 4,000 km (2,500 mile) border and their troops faced off for three weeks last month on a windswept Himalayan plateau where they fought a brief but bloody war in 1962.

Pakistan and India have fought three wars, two of them over disputed Kashmir.

India has responded cautiously to Li's overtures, partly because of China's friendship with Pakistan. For its part, Beijing is concerned about India's growing relations with the United States.

"I wish to reiterate solemnly China's continue firm support to Pakistan in its efforts to uphold independence, sovereignty and territorial integrity," Li said in a possible reference to India and to the United States, which angers many with drone strikes targeting militants in Pakistan.

Pakistan is going through a turbulent chapter in its ties with the United States, which plans to withdraw most of its troops from neighboring Afghanistan in 2014. Many U.S. officials have questioned Pakistan's commitment to fighting Islamic militancy since U.S. forces tracked down and killed Osama bin Laden in a garrison town near Islamabad two years ago.

"Being a close friend of China, Pakistan wishes it well" in its attempts to address its border and security concerns, Pakistan's Nation newspaper said in an editorial.

"It is also good that Premier Li is not oblivious to the kind of ill-will resulting from the core issue of Kashmir."

In a brief security scare in southern Karachi on Tuesday, a roadside bomb exploded near the seafront which police said was likely aimed at a passing van full of Chinese port workers. No one was hurt.

(Editing by Raju Gopalakrishnan)

By Alice Mannette Ian Simpson

MOORE, Oklahoma (Reuters) - Pre-dawn emergency workers searched feverishly for survivors in the rubble of homes, primary schools and an hospital in an Oklahoma City suburb ravaged by a massive Monday afternoon tornado feared to have killed up to 91 people and injured well over 200 residents.

The 2-mile(3-km) wide tornado tore through town of Moore outside Oklahoma City, trapping victims beneath the rubble as one elementary school took a direct hit and another was destroyed.

Reporters were cleared back from Plaza Towers Elementary School, which sustained a direct hit Oklahoma Lieutenant Governor Todd Lamb told CNN. But television pictures showed firefighters from more than a dozen fire departments working under bright spotlights to find survivors.

President Barack Obama declared a major disaster area in Oklahoma, ordering federal aid to supplement state and local efforts in Moore after the deadliest U.S. tornado since one killed 161 people in Joplin, Missouri, two years ago.

The White House said Obama would make a statement on the Oklahoma tornado at 10 a.m. EDT (1400 GMT). It said the president was brieved overnight on the tornado tragedy.

There was an outpouring of grief on Plaza Towers' Facebook page, with messages from around the country including one pleading simply: "Please find those little children."

A separate Facebook page set up to reunite people in the area hit by a tornado on Sunday with their belongings and pets also showed entries for Moore residents overnight.

Another elementary school, homes and a hospital were among the buildings leveled in Moore, leaving residents of the town of about 50,000 people stunned at the devastation and loss of life. Many residents were left without power and water.

The Oklahoma medical examiner said 20 of the 91 expected to have been killed were children. The office had already confirmed 51 dead and had been told during the night by emergency services to expect 40 more bodies found in the debris, but had not yet received them.

At least 60 of the 240 people injured were children, area hospitals said.

The National Weather Service assigned the twister a preliminary ranking of EF4 on the Enhanced Fujita Scale, meaning the second most powerful category of tornado with winds up to 200 mph.

Witnesses said Monday's tornado appeared more fierce than the giant twister that was among the dozens that tore up the area on May 3, 1999, killing more than 40 people and destroying thousands of homes. That tornado ranked as an EF5, meaning it had winds over 200 mph.

The 1999 event in Oklahoma ranks as the third-costliest tornado in U.S. history, having caused more than $1 billion in damage at the time, or more than $1.3 billion in today's dollars. Only the devastating Joplin and Tuscaloosa tornadoes in 2011 were more costly.

"I am close to the families of all who died in the Oklahoma tornado, especially those who lost young children. Join me in praying for them," Pope Francis said in a Twitter message.

Jeff Alger, 34, who works in the Kansas oil fields on a fracking crew, said his wife Sophia took their children out of school when she heard a tornado was coming and then fled Moore and watched it flatten the town from a few miles away.

"They didn't even have time to grab their shoes," said Alger, who has five children aged four to 11. The storm tore part of the roof off of his home. He was with his wife at Norman Regional Hospital to have glass and other debris removed from his wife's bare feet.

Moore was devastated with debris everywhere, street signs gone, lights out, houses destroyed and vehicles tossed about as if they were toys.

The dangerous storm system threatened several southern Plains states with more twisters. The area around Moore faces the risk of severe thunderstorms on Tuesday, which could hamper rescue efforts.

STORM ALERTS

Speaking outside Norman Regional Hospital Ninia Lay, 48, said she huddled in a closet through two storm alerts and the tornado hit on the third.

"I was hiding in the closet and I heard something like a train coming," she said under skies still flashing with lightning. The house was flattened and Lay was buried in the rubble for two hours until her husband Kevin, 50, and rescuers dug her out.

"I thank God for my cell phone, I called me husband for help."

Her daughter Catherine, seven, a first-grader at Plaza Towers Elementary School, took shelter with classmates and teachers in a bathroom when the tornado hit and destroyed the school. She escaped with scrapes and cuts.

SCHOOL DESTROYED

The National Weather Service Storm Prediction Center provided the town with a warning 16 minutes before the tornado touched down at 3:01 p.m. (2001 GMT), which is greater than the average eight to 10 minutes of warning, said Keli Pirtle, a spokeswoman for the center in Norman, Oklahoma.

The notice was upgraded to emergency warning with "heightened language" at 2:56 p.m., or five minutes before the tornado touched down, Pirtle said.

Television media measured the tornado at more than 2 miles wide, with images showing entire neighborhoods flattened.

The U.S. Federal Aviation Administration (FAA) imposed a temporary flight restriction that allowed only relief aircraft in the area, saying it was at the request of police who needed quiet to search for buried survivors.

Oklahoma activated the National Guard, and the U.S. Federal Emergency Management Agency activated teams to support recovery operations and coordinate responses for multiple agencies.

Briarwood Elementary School, which also stood in the storm's path, was all but destroyed. On the first floor, sections of walls had been peeled away, giving clear views into the building; while in other areas, cars hurled by the storm winds were lodged in the walls.

The number of injured as reported by several hospitals rose rapidly throughout the afternoon.

"The whole city looks like a debris field," Glenn Lewis, the mayor of Moore, told NBC.

"It looks like we have lost our hospital. I drove by there a while ago and it's pretty much destroyed," Lewis said.

The massive twister struck at the height of tornado season, and more were forecast. On Sunday, tornadoes killed two people and injured 39 in Oklahoma.

(Additional reporting by Lindsay Morris, Carey Gillam, Nick Carey, Brendan O'Brien and Greg McCune; Writing by Daniel Trotta and Nick Carey; Editing by Alison Williams and W Simon)

By Mike McDonald

GUATEMALA CITY (Reuters) - Guatemala's highest court on Monday overturned a genocide conviction against former dictator Efrain Rios Montt and reset his trial back to when a dispute broke out a month ago over who should hear the case.

Rios Montt, 86, was found guilty on May 10 of overseeing the killings by the armed forces of at least 1,771 members of the Maya Ixil population during his 1982-83 rule. He was sentenced to 80 years in prison.

However, in a ruling on Monday, the country's Constitutional Court ordered that all the proceedings be voided going back to April 19, when one of the presiding judges suspended the trial because of a dispute with another judge over who should hear it.

It was unclear when the trial might restart.

Rios Montt's conviction was hailed as a landmark for justice in the Central American nation, where as many as 250,000 people were killed in a bloody civil war lasting from 1960 to 1996.

When Rios Montt was in power, his government launched a fierce offensive in which soldiers raped, tortured and killed tens of thousands of Maya villagers suspected of helping Marxist rebels. Thousands more were forced into exile or had to join paramilitary forces fighting the insurgents.

After he was sentenced, a court ordered the government to apologize for atrocities committed against indigenous people.

Ana Caba, an ethnic Ixil who survived the civil war after fleeing her home, was stunned by the Constitutional Court's decision.

"I'm distressed," she told Reuters. "I don't know what's happening. That's how this country is. The powerful people do what they want and we poor and indigenous are devalued. We don't get justice. Justice means nothing for us."

IRREGULARITIES

At the time the row broke out between the judges, a number of appeals were lodged with the Constitutional Court over alleged irregularities in the handling of the case.

One related to Francisco Garcia, one of Rios Montt's defense lawyers, who had just won an appeal to be readmitted to the case. Garcia was thrown out when the trial began for repeatedly trying to have two of the three presiding judges recused.

When Garcia was reinstated, he tried to recuse the judges again, but they rejected his bid and proceeded with the case.

The Constitutional Court said the judges should have suspended the trial until the recusal attempt had been officially resolved. A spokesman for the court could not say how the recusal bid needed to be formally settled.

Diana Cameros, a psychologist who attended the Rios Montt trial, attacked the Constitutional Court over its ruling.

"It's absurd," she told Reuters. "It said in a previous ruling that the process couldn't be wound back to stages that had already concluded, and now it's saying something that contradicts what they said before."

The court said it had given the judges who sentenced Rios Montt 24 hours to comply with its order.

After spending a couple of nights in prison, Rios Montt was transferred to a hospital last week for treatment for respiratory and prostate problems.

He came to power in a bloodless coup on March 23, 1982, and ruled for 17 months during one of the most brutal phases of the conflict until he was toppled in August 1983. He has repeatedly denied the charges against him.

Former U.S. President Ronald Reagan supported Rios Montt's government and said in late 1982 that the dictator was getting a "bum rap" from rights groups for his military campaign against left-wing guerrillas during the Cold War.

Reagan also once called Rios Montt "a man of great personal integrity."

The retired general returned to politics after his fall from power and later unsuccessfully ran for president. For years, he avoided prosecution because he had immunity as a congressman. That ended when he left Congress in 2012.

Until August 2011, when four Guatemalan soldiers received 6,060-year prison sentences for mass killings in the northern village of Dos Erres in 1982, no convictions had been handed down for massacres carried out during the war.

(Reporting by Mike McDonald; Editing by Dave Graham, Kieran Murray and David Brunnstrom)