Nigeria's army on Sunday extended by 24 hours a travel ban imposed on Borno, the restive northeastern state worst hit by Boko Haram attacks.

Nigerian President Goodluck Jonathan said Saturday that killings by militants of Boko Haram and other Islamists across the globe, including those who killed a British aid worker, have no religious basis.

"What is happening globally now has no religious basis," Jonathan told visiting Muslim leaders on the occasion of Eid al-Adha, the Muslim feast of sacrifice. "Only yesterday, a British aid worker was slaughtered by ISIS, and that is not Islamic."

Nigeria's military on Friday dismissed claims that a man beheaded by Boko Haram fighters in the group's latest video was an air force pilot in a fighter jet that went missing three weeks ago.

Boko Haram leader Abubakar Shekau had claimed in the footage obtained by Agence France-Presse on Thursday that militants shot down the Alpha Jet and showed wreckage of an aircraft which included the Nigerian Air Force's green and white roundel.

Nigeria's embattled northeast Yobe state on Friday imposed a travel ban through the Muslim holiday weekend to guard against Boko Haram attacks, barring motorists from reaching their families for the Eid celebration.  

A message broadcast on public radio in Yobe instructed people "to remain in their towns and villages until Monday... to forestall security breaches as we celebrate the Eid" holiday.

Boko Haram leader Abubakar Shekau dismissed Nigerian military claims of his death in a new video obtained by AFP on Thursday and said the militants had implemented strict Islamic law in captured towns.

"Here I am, alive. I will only die the day Allah takes my breath," Shekau said, adding that his group was "running our... Islamic caliphate" and administering strict sharia punishments.

Nigeria's ruling party has given President Goodluck Jonathan a free run for a second term of office at next year's elections but he faces a potential sticking point: is he even eligible?

At least two cases to stop Jonathan from standing are currently before the courts, citing a clause in the constitution that prevents anyone from swearing the oath of office more than twice.

Social and economic development has long been touted as the way to revive the fortunes of Nigeria's impoverished north and prevent legions of disaffected young men turning to radical Islam.

But Boko Haram violence has scuppered progress, particularly from one potentially lucrative source of revenue -- the oil found under the Lake Chad Basin in the country's far northeast.

The United States voiced skepticism Thursday over reports from the Nigerian military that Boko Haram leader Abubakar Shekau had been killed in recent clashes with troops.

"The Nigerians have announced several times that the head of Boko Haram was dead and every single time we find out that it is not true," a senior State Department official told reporters.

Nigeria's police on Thursday claimed that one of more than 200 schoolgirls kidnapped by Boko Haram militants nearly six months ago had been found, but elders rejected the claim.

National police spokesman Emmanuel Ojokwu said the girl was "dropped off by suspected Boko Haram militants at Mubi in Adamawa state" at about 5:00 pm (1600 GMT) on Wednesday.

A Nigerian military claim that Boko Haram leader Abubakar Shekau was dead was dismissed as propaganda on Thursday by analysts, who said that even if true it was unlikely to undermine the militants.

The defense ministry said on Wednesday that Shekau was dead and that one Bashir Mohammed, killed during recent clashes with troops, was a lookalike who had been impersonating him in videos.