Myanmar released about 20 political prisoners on Friday, a top official said, hours before its reform-minded leader was due to leave on a landmark visit to the United States to meet President Barack Obama.

President Thein Sein, a former general, has freed hundreds of political detainees since coming to power in early 2011 as part of sweeping changes that have led to the end of most Western sanctions.

Twin bomb attacks on Friday killed at least eight people outside mosques in northwest Pakistan, where the party of cricket star Imran Khan is forming a coalition government, officials said.

The blasts took place near two mosques in the Baazdara area of northwestern Malakand region, senior local administration official Amjad Ali Khan told Agence France Presse.

Sixty-two people were injured when multiple cars derailed on Hong Kong's light railway in the north of the city, throwing passengers onto the floor, police said Friday.

"There was a derailment on the light rail," a police spokeswoman told Agence France Presse, confirming that 62 people were injured in the accident which occurred in the New Territories region north of the city's business district.

The U.S. on Friday called for the release of two Vietnamese activists jailed for distributing anti-government leaflets, saying their case highlights a "disturbing trend" of authorities muzzling dissent.

University student Nguyen Phuong Uyen, 21, was jailed for six years, while computer technician Dinh Nguyen Kha, 25, was imprisoned for eight years by a court in southern Long An province on Thursday.

Uniformed gunmen in South Sudan went on a rampage in a key hospital, destroying drug supplies and ransacking wards, Doctors Without Borders (MSF) said Friday, warning the attack leaves some 100,000 people without lifesaving healthcare.

As well as looting drugs, beds and equipment, the attackers' "extraordinary...systematic and purposeful damage to the infrastructure" has left the hospital unusable without major repairs, MSF said Friday, after visiting the wreckage for the first time since the attack.

A clan whose chiefs are on trial for the Philippines' worst political massacre secured big wins in local elections this week, results showed Friday, deepening fears that justice may never be served.

Leaders of the Ampatuan family and their gunmen are accused of massacring 58 people, including 32 journalists, in the southern province of Maguindanao more than three years ago in a bid to quash a rival's challenge to become governor.

A 5.9-magnitude quake struck off a remote area of the Solomons Islands Friday, but no tsunami warning was issued for the Pacific nation and a seismologist said there was no cause for concern.

The United States Geological Survey said the tremor, at a depth of 13 kilometers (eight miles), struck in the Santa Cruz Islands at 06:43 GMT about 93 kilometers southwest of Lata.

Three Chinese government ships entered the waters of disputed islands on Friday, Japan's coastguard said, more than a year after the then-Tokyo governor set off the row by announcing plans to buy them.

The Chinese maritime surveillance vessels were spotted off the Senkaku islands, which China calls the Diaoyus, in the East China Sea at around 2:30 pm (05:30 GMT), the coastguard said.

Iran's firebrand President Mahmoud Ahmadinejad will address a forum on water security in Thailand next week, an embassy official said on Friday, just weeks before he stands down from the post.

His scheduled appearance in the northern Thai city of Chiang Mai from Sunday comes as Iran gears up for elections and as world powers press the Islamic republic over its suspected nuclear program and support for the Syrian regime.

President Thein Sein's historic invitation to the White House is an endorsement of "Myanmar's Spring" and a further sign that the former pariah's reforms are irreversible, a senior Myanmar official said.

Washington will welcome the former general on Monday in a hugely symbolic reward for sweeping changes since he took power two years ago. He will be the first leader of the former military-ruled nation to visit since 1966.