A wave of violence hours after Nigeria's government announced a truce with Boko Haram raised doubt about whether more than 200 schoolgirls kidnapped by the Islamist militants will be released, deflating the new hopes of their parents.

Nigeria's armed forces chief, Air Chief Marshal Alex Badeh, announced the ceasefire on Friday to enable the release of the girls, who were abducted from the remote north-eastern village of Chiboke in April.

But Boko Haram has not confirmed the truce and there have been at least five attacks since that have killed dozens. Security sources say the insurgents are to blame for the attacks. Talks were scheduled to continue in neighbouring Chad today.

"We were jubilating. We had every reason to be happy ... but since then the ceasefire has been broken in quite a number of places already," Lawan Abana, a parent of the one of the missing girls, said. He added that there were doubts about the credentials of the reported Boko Haram negotiator Danladi Ahmadu, who was unheard of before.

"Can we trust him that he can deliver on this promise of releasing the girls when he has not delivered on the promise of the ceasefire?" Mr Abana said.

The government says the attacks may not have been Boko Haram but one of several criminal groups exploiting the chaos of its insurgency.

Analysts point out that Boko Haram is anyway heavily factionalised, so what matters is whether the faction the government is talking to has control over the girls' fate.

"Boko Haram is deeply fractured. The Nigerian government has had a ... difficult time identifying a Boko Haram representative who could make compromises and guarantee the entire group will observe them," risk consultancy Stratfor said in a note.

"It is quite possible that Abuja has reached an agreement with a legitimate representative of a specific cell ... that holds the kidnapped schoolgirls captive," it said at the weekend.