Nearly 900 children held by a pro-government militia force fighting Boko Haram insurgents in northeastern Nigeria were freed on Friday, the UN said.

Two people, including a soldier and a vigilante, were killed when two female suicide bombers detonated their explosives in northeast Nigeria's Borno state, military and militia sources said Friday.

The bombers quickly blew themselves up on Thursday in bid to evade arrest when they were stopped by troops and militiamen outside the garrison town of Monguno.

A three-storey residential building collapsed Wednesday in a densely-populated part of Lagos, and local media said there could be many casualties, including schoolchildren.

More than 300 people were arrested on suspicion of committing electoral offences during Nigeria's recent elections, the top police chief has said. 

Nigeria's opposition leader on Wednesday rejected the re-election of President Muhammadu Buhari in a delayed poll plagued by claims of rigging, vowing to challenge the "sham" result in court.

Muhammadu Buhari was re-elected Nigeria's president, results showed Tuesday, after a delayed poll that angered voters and led to claims of rigging and collusion.

Nigerian police on Saturday said many people were feared dead after a petrol tanker veered off the road, caught fire and exploded as people tried to recover fuel.

The vehicle crashed in the Odukpani area of the southeastern state of Cross River, just north of the state capital, Calabar, at about 5pm (1600 GMT) on Friday.

A cholera outbreak in north-eastern Nigeria has claimed nearly 100 lives over the past two weeks, the United Nations said Saturday.

More than 3,000 cholera cases have been recorded in the states of Yobe and Borno in a region that is also grappling with a Boko Haram insurgency, it said.

Nigeria has declared a national disaster after severe flooding left about 100 people dead across 10 states, the country's main relief agency said on Tuesday.

Britain will give Nigeria aid worth £200 million over five years to help it cope with the brutal insurgency being waged by Boko Haram jihadists, the foreign ministry in London said Wednesday.