Abuja (AFP) – Five members of the Nigerian Air Force have been killed when a helicopter crashed while Boko Haram militants ambushed a military base Nigeria's northeastern region, a spokesman said Thursday.

The air force spokesman, Ibikunle Daramola, said the five crew members had died when the helicopter "crashed into combat" on January 2 while he was providing close air support to troops fighting the Boko Haram attack in Damasak, a town close to the border with Niger.

Among the victims were two pilots, two gunners and a flight technician, he said.

The attack was one of four raids on military posts this week in a region devastated by jihadist violence, which particularly targeted in recent months the troops in the Borno and Yobe states in the north-east of the country.

The four raids were claimed by a Boko Haram faction called ISWAP, the Islamic State of West Africa, which reportedly killed 14 soldiers and took another hostage, according to the group. SITE intelligence unit that monitors jihadist activities.

Details are rare on the ground helicopter, but if the jihadists were shooting at it, it would indicate that they now have more sophisticated weapons than those used in the last four years of fighting.

Since July, Boko Haram attacks against military bases have increased, almost all in the region around Lake Chad.

In November, militants raided a base in the Nigerian village of Metele, near the Nigerian border, killing at least 44 people, although the surviving soldiers have more than 100 dead.

In the run-up to the February elections, the Nigerian army insisted that the situation was under control, rarely revealing the number of casualties, with the exception of Wednesday's crash.

President Muhammadu Buhari, who came to power in 2015 with the promise to end the violence, is under increasing pressure to act as a result of the recent wave of attacks.

He will try to be reelected at the ballot on February 16th.

The bloody insurgency of Boko Haram began in northeastern Nigeria in 2009, but has since spread to neighboring countries, provoking a regional military response.

In Nigeria alone, more than 27,000 people have been killed in the past decade and some 1.8 million people have been forced to leave their homes because of the violence.