BBC News with Jonathan Izard

President Obama has mounted a strong defence of his controversial use of unmanned aircraft to hit militant targets abroad. In a major speech on counter-terrorism, the president said drone strikes were effective and legal, but he stressed they should be used only when faced with imminent threats. Paul Adams reports from Washington.

With greater frankness than ever before, the president discussed his administration's guidelines for the use of unmanned drone strikes to kill members of al-Qaeda and its affiliates. He said they could only be used in the context of what he called "continuing imminent threats" to Americans and when there was near certainty that no innocent civilians would be affected. And he listed a number of specific steps to make good on his long-standing pledge to close the military detention facility at Guantanamo Bay in Cuba and identifying a place in the United States where military commissions can take place.

British security sources say the two men who hacked a soldier to death in the full public gaze on a London street on Wednesday had been investigated in the past because of terrorist suspicions but were no longer under surveillance. One of them has been identified as Michael Adebolajo, a British man of Nigerian origin who converted to Islam 12 years ago. Both men remain under armed police guard in hospital after being shot by police. Here's our security correspondent Frank Gardner.

It's reassuring that both of the Woolwich murder suspects were already known to the security services, but it's also a cause for concern that they were no longer under surveillance. It emerged that in the past both men had been the subjects of a security service investigation, but somewhere between MI5 deciding that these men did not pose a threat to national security, and the events of yesterday something changed and MI5 missed it - what were classed as radical views had turned into violent action, and there was no one close enough to the men to stop it.

The victim of the attack has been named as 25-year-old British soldier Lee Rigby, who had served two tours in Afghanistan.

Militants in Niger have killed more than 20 people in two almost simultaneous suicide car bomb attacks targeting a military barracks and a uranium mine in the north of the country. Most of the casualties were soldiers who died in the attack on a barracks in Agadez. Separately one worker was killed and others injured when insurgents targeted a uranium mine run by the French nuclear group Areva. Our West Africa correspondent Thomas Fessy has been following events.

A spokesperson for the French company Areva said a team was going to assess the damage of the uranium sites of Arlit, but production has stopped for now. According to government and local sources, the crushing and grinding units were particularly hit as a result of the suicide bomb attack. Areva wouldn't confirm whether it was planning to withdraw its staff from the sites while activities are suspended. In Agadez, where the army barracks was targeted by militants, security forces have cordoned off several areas in the town according to residents.

World News from the BBC

A leading figure in the Syrian opposition has presented a plan for President Assad and his family to be given a safe exit if he stands down - something the president has repeatedly said he won't do. Ahmed Moaz al-Khatib, the outgoing leader of the Syrian National Coalition, said the Syrian president would have 20 days to accept the offer.

Thousands of people gathered in the southern Nigerian town of Ogidi for the funeral of the writer Chinua Achebe, who's been described as the father of modern African literature. From Nigeria Will Ross has this report.

I doubt the church here in Ogidi town has seen anything like it. Thousands of people flocked here. They were coming to pay tributes to Chinua Achebe, who died at the age 82 earlier this year. Many of the people who come to here took shelter under the trees and under tents because there was simply no room inside. The President of Nigeria Goodluck Jonathan was here, and he paid a tribute to Chinua Achebe, and he also referred to some of his books, including one called The Problem with Nigeria, in which the writer summed up the problem of the country in one word: leadership.

The Russian Environment Minister Sergei Donskoi has ordered all 16 workers at a scientific research base in the Arctic Ocean to make plans to evacuate. The minister said the precautions were necessary because the station was surrounded by melting ice. Russian officials said a nuclear-powered icebreaking ship was being brought in to move the station onto an island.

For the second time during this year's Canne Film Festival, thieves have pulled off an audacious jewelry heist at the France resort. A diamond necklace worth more than $2m was stolen at a glitzy party attended by film stars including Sharon Stone on Tuesday's night. The jewellers De Grisogono said the item was one of 20 paraded by models at the event which had been protected by police, bodyguards and hotel security staff. They admitted they didn't know how the item had been taken. On the opening night, thieves stole millions of dollars worth of gems from a hotel's safe.