Nigeria's military and presidency on Friday claimed to have reached a deal with Boko Haram militants on a ceasefire and the release of more than 200 kidnapped schoolgirls.

"A ceasefire agreement has been concluded between the Federal Government of Nigeria and the Jama'atu Ahlis Sunna Lidda'awati wal-Jihad (Boko Haram)," Chief of Defence Staff Air Marshal Alex Badeh said.

"I have accordingly directed the service chiefs to ensure immediate compliance with this development in the field."

Separately, President Goodluck Jonathan's Principal Secretary Hassan Tukur told AFP that an agreement to end hostilities had been reached following talks, as well as the release of 219 girls held captive since April.

Tukur said that he had represented the government at two meetings with the Islamist rebels in neighbouring Chad mediated by that country's President Idriss Deby.

"Boko Haram issued the ceasefire as a result of the discussions we have been having with them," said Tukur, adding that the announcement was made "last night", Thursday.

"They have agreed to release the Chibok girls," he continued, referring to the 219 teenage girls held hostage after their April 14 kidnapping from a secondary school in Chibok, northeast Nigeria.

But questions surrounded the purported deal, given that Jonathan is expected to declare his re-election bid and positive news about the hostages and violence could give him a political boost.

There was also uncertainty about the identity of Danladi Ahmadu, who was said by Tukur to be Boko Haram's representative at the talks and who gave a radio interview broadcast on Friday morning.

Multiple analysts cast doubt on Ahmadu's credibility as a Boko Haram envoy while Nigeria has made similar ceasefire claims in the past which failed to materialise.

"I have never heard of such a man (Ahmadu) and if Boko Haram wanted to declare a ceasefire it would come from the group's leader Abubakar Shekau," said Shehu Sani, a Boko Haram expert who has negotiated with the group before on behalf of the government.

"This whole thing is hoax. Ahmadu is not a part of Boko Haram," said another source with intimate knowledge of the group.