MAIDUGURI, Nigeria (Reuters) - Militants killed around 100 Nigerian soldiers in an attack on an army base on Sunday, security sources said on Thursday, blaming Islamic State West Africa.

The toll is among the highest since President Muhammadu Buhari came to power in 2015 and it could raise pressure on him ahead of an election in February, not least because he has claimed victory over the nine-year insurgency.

The insurgents attacked the base in the village of Metele in northeastern Borno state, the epicentre of a revolt by Boko Haram and its Islamic State splinter group.

“The insurgents took us unawares,” said an officer who requested anonymity. “The base was burned with arms and we lost about 100 soldiers. It is a huge loss.”

Many troops are missing, the sources said. One soldier said more troops were killed on Tuesday when an attempt to recover bodies from the initial attack was ambushed.

“We all flew because we didn’t know where the bullets were coming from,” he said. “They killed some of us who went to evacuate the bodies of the killed soldiers.”

“We left our amour, tanks and weapons. They were all there. The village is still under their control.”

Four security sources said around 100 died in Metele and the death toll was not final. The fifth said 96 died in the northeast in recent days, mostly in Metele.

The senate, which is controlled by the opposition People’s Democratic Party (PDP), on Thursday suspended its session in honour of what it said were 44 dead soldiers after the Metele attack.

Opposition presidential candidate Atiku Abubakar, who is Buhari’s main rival, called on the government to support the families of dead soldiers.

A presidency spokesman said the military would issue a statement. Military spokesmen did not respond to requests for comment. The government and military often decline to acknowledge the scale of losses in the northeast.

Militants have killed hundreds of soldiers in the region in recent months.