Nigeria military helicopter crashes in restive northeast

YOLA Nigeria (Reuters) - A Nigerian military helicopter crashed and exploded on Thursday in the northeast region of the country where it is battling Boko Haram Islamist insurgents, witnesses and a security source told Reuters.

The security source in the capital Abuja, said there were some casualties but declined to give further details saying the Nigerian defence ministry would issue a statement later. The incident occurred, however, in an area where there were no immediate reports of combat or of Boko Haram activity.

Boko Haram, which seeks to establish a caliphate in religiously mixed northern Nigeria, has stepped up attacks since the government announced a purported ceasefire last month which was later rejected by the group's leader.

It was the second Nigerian military helicopter to go down this week in Yola, in Adamawa State, after another, according to the defence ministry, made a forced landing shortly after takeoff.

Hey Ibrahim Ali a resident of Hayin Kada village near Yola, told Reuters they saw the helicopter hovering.

"Then later, we heard the sound of the helicopter suddenly changed, it started going down and then we heard a loud sound, followed by several explosions. So we started running into the bush," Ali said by telephone.

He said villagers went to the crash site on Friday morning and it was cordoned off by security officials.

The helicopter may have been heading for a military operation further north from Yola where the military were fighting Boko Haram. The army retook control of the towns of Mubi and Maiha from the insurgents with the help of local hunters and civilian vigilantes on Thursday.

But there was still signs of rebel activity near this area.

About 30 Boko Haram militants stormed the village of Chibok, in Borno State, where the group abducted some 200 schoolgirls seven months ago, raising international outcry. Chibok has been target of a number of attacks since the abductions.

"The insurgents arrived at about 5pm on Thursday, shooting sporadically, forcing people to flee into the bush," a villager who fled told Reuters by telephone, adding that many villagers may have been killed.

He said the militants burnt several houses and were moving towards neighbouring Damboa.

(Reporting by Isaac Abrak and Felix Onuah in Abuja, Lanre Ola in Maiduguri, Imma Ande in Yola and Tife Owolabi in Yenagoa; Writing by Bate Felix)