U.S. President Barack Obama on Saturday hailed the "extraordinary sacrifices" made by the 31 U.S. soldiers killed in Afghanistan when, according to local officials, the Taliban shot down their helicopter.

Obama also paid tribute to the seven Afghan soldiers killed during an anti-Taliban operation late Friday when a rocket fired by the insurgents struck their Chinook helicopter in Wardak province, southwest of the capital Kabul.

Newly independent South Sudan swore in its MPs on Saturday, two days ahead of parliament's opening session, with the speaker calling for cooperation regardless of background or political affiliation.

"You are the founders of the first ever parliament of the Republic of South Sudan," James Wani Igga told the National Legislative Assembly.

Islamist forces pulled out of many of their bases in the Somali capital of Mogadishu overnight, government and rebel spokesmen said Saturday.

"The information we are receiving is that there is a retreat from the city. This is a golden victory for the Somali people and we are committed to ensure that peace and order is restored to those areas," said government spokesman Abdirahman Omar Osman.

A total of 31 members of the U.S. special forces have died in a helicopter crash in eastern Afghanistan along with seven Afghans, a statement from Afghan President Hamid Karzai's office said Saturday.

"The president of the Islamic Republic of Afghanistan Hamid Karzai expressed condolences over a NATO helicopter crash and the deaths of 31 members of U.S. special forces," the statement said.

A member of a rogue U.S. Army unit was sentenced to three years' prison Friday after pleading guilty to killing an unarmed Afghan civilian in U.S. custody in May 2010.

Specialist Adam Winfield, 23, of Coral Gables, Fla., had been charged with premeditated murder, aggravated assault and conspiracy to commit murder in several incidents, including the deaths of three Afghan civilians in Kandahar Province.

The Japanese city of Hiroshima marked the 66th anniversary of the bombing on Saturday, as the nation fights a different kind of disaster from atomic technology — a nuclear plant in a meltdown crisis after being hit by a tsunami.

The site of the world's first A-bomb attack observed a moment of silence at 8:15 a.m. Saturday (2315 GMT Friday) — the time the bomb was dropped on Aug. 6, 1945, by the United States in the last stages of World War II.

The U.S. Army will shorten the length of tours of duty for personnel deployed in combat zones from a year to nine months, as it pursues its withdrawal from Iraq and Afghanistan, the Pentagon said Friday.

"This policy will not affect personnel or units currently deployed or deploying prior to Jan. 1, 2012," the secretary of the army, John McHugh, said in a statement, adding the move would be fully in effect by April 2012.

Venezuelan President Hugo Chavez said Friday that he has asked legislators to give him permission to return to Cuba for a second round of chemotherapy for his cancer.

The National Assembly's secretariat announced that the body would hold a special session Saturday to vote on authorization for Chavez to leave the country.

Gunmen opened fire killing five people on Friday as they looted food aid for thousands of starving people affected by famine in the Somali capital, officials and witnesses said.

"Five people died on the spot after militiamen opened fire to loot the food aid," said Abdikadir Mohamed, a driver.

Sweden has drawn up a plan to fight extremism in response to attacks in neighboring Norway that killed 77 people last month, government ministers wrote in an opinion piece published Friday.

The national plan was needed to safeguard Sweden against similar attacks, Prime Minister Fredrik Reinfeldt and two ministers wrote, describing the Norway killings as a "catastrophe of unimaginable dimensions".