Sudanese authorities released six political prisoners early on Tuesday, an Agence France Presse photographer reported, after President Omar al-Bashir vowed to free all political detainees.

The six men walked free to tearful relatives waiting outside Kober Prison in Khartoum North.

North Korea vowed Tuesday to restart all mothballed facilities at its main Yongbyon nuclear complex, adding to tensions already raised by near daily warlike threats against the United States and South Korea.

The reactor was shut down in 2007 as part of international nuclear disarmament talks that have since stalled.

Dozens of gunmen attacked an electricity plant in northwest Pakistan, killing seven people and disrupting power to 100,000 people overnight, officials said Tuesday.

It was the latest audacious assault underscoring rising violence in the northwest as Pakistan prepares to hold general and provincial elections on May 11, which are due to mark the country's first democratic transition of power.

A foreign man and woman studying Portuguese in Brazil were held for hours while the woman was sexually assaulted aboard a public transport van they boarded over the weekend in Rio de Janeiro's showcase Copacabana beach neighborhood, police said in a statement.

Two men aged 20 and 22 were taken into custody and a third was being sought in connection with the attack, which saw the pair held for around six hours starting shortly after midnight on Saturday, police said.

A fire killed 13 students at a Muslim school in Myanmar's main city on Tuesday, police said, raising tensions in the wake of sectarian clashes despite police assurances that the blaze was accidental.

The government called for calm and sent security forces to the scene after an angry crowd gathered demanding answers about the deadly fire in Yangon, which follows a wave of Buddhist-Muslim killings and arson in central Myanmar.

The United States has placed a destroyer off the South Korean coast to defend against a possible missile strike, the latest in a series of publicized U.S. deployments to counter North Korean threats.

The USS Fitzgerald was moved to the southwestern coast after taking part in annual military exercises, instead of returning to its home port in Japan, a U.S. defense official told Agence France Presse Monday on condition of anonymity.

President Joyce Banda on Monday said Malawi was giving up on mediation efforts and would take to the courts to settle a long dormant border dispute with Tanzania which has been re-activated by prospects of an oil find.

"Our view is that we should eventually go to court. We should not waste time on this (mediation)," Banda told reporters in Lilongwe on return from visits to the United States and Britain.

The White House said Monday that despite days of bellicose rhetoric, North Korea had yet to back up its threats with mass troop mobilizations or troop movements.

With tensions on the Korean peninsula rising ever higher, Washington reiterated that it took Pyongyang's war talk seriously but also noted that threats and warnings were nothing new from the isolated state.

Around 11 people were killed after fresh fighting between government forces and a militia in the eastern Democratic Republic of Congo, the United Nations said Monday.

U.N. spokesman Eduardo del Buey said the APCLS militia suffered the reported fatalities, while a soldier from the DR Congo army was injured during the skirmishes in Kitchanga, in North Kivu province.

Serbian President Tomislav Nikolic on Monday cast doubt on whether a final agreement with breakaway Kosovo is attainable, a day ahead of highly anticipated EU-sponsored talks with the Pristina leadership in Brussels.

"Intractable statements from Pristina put us before a fait accompli and are not encouraging," Nikolic told reporters ahead of Tuesday's meeting.