MAIDUGURI, Nigeria: Nigerian troops backed by air strikes were fighting on Monday to recapture the northeastern town of Monguno from Boko Haram insurgents who had seized it a day earlier, security sources said.

The insurgents had launched several simultaneous attacks early on Sunday. One hit the outskirts and airport of the main northeastern city of Maiduguri, the birthplace of Boko Haram’s five-year-old insurgency.

They then hit two other towns, including Monguno, which lies on the shores of Lake Chad.

A defense spokesman said on Sunday evening that airstrikes had been carried out take back the town after ground troops were forced to retreat.

“The operation resumed on Monguno this morning through air bombardment to dislodge the insurgents,” a security source said on Monday.

More than 100 people, mainly insurgents, died in fighting, a local journalist counting bodies at the biggest morgue said on Monday.

The local reporter, Bello Dukku, said by telephone that , the dead also included at least 15 soldiers and a few civilians.

Dukku said he had had to leave the morgue after counting 100 bodies, because of the overwhelming stench. He said another 50 people had been injured in the fighting.

Soldiers in Monguno said on Sunday they had fled because of the insurgents’ superior fire power.

Monguno lies near the larger town of Baga, where a military base was taken over by Boko Haram in early January in an attack that left scores of civilians dead.

In a subsequent video, the insurgents claimed responsibility for the capture of Baga and said they had seized enough weapons to “annihilate Nigeria.”

The conflict has intensified in the past year and the government’s handling of the security situation is major issue in the campaign for a presidential election on Feb. 14, which pits President Goodluck Jonathan against former military ruler Muhammadu Buhari.

In a visit to Nigeria on Sunday, US Secretary of State John Kerry said the United States was committed to helping Nigeria fight Boko Haram but its ability to do so would hinge on how the well election is conducted.

Security analysts believe Boko Haram’s capture of Monguno — after the Lake Chad fishing hub of Baga was captured earlier this month — was driven by a need for food, fuel, medicine and other essentials.

Hundreds of people, if not more, are feared to have been killed in Baga, where Boko Haram fighters destroyed much of the town and razed at least 16 surrounding settlements.

Residents who fled Baga have said Boko Haram has enough supplies from the abandoned and looted markets to last for months, but they will eventually be forced to push south.

Ryan Cummings, chief Africa analysts at risk consultants Red24, suggested the Monguno attack was also likely prompted by the need for weapons to counter eventual offensives by regional armies.

Boko Haram violence has effectively wiped large parts of northeast Nigeria off the electoral map, making voting impossible in next month’s presidential and parliamentary poll.

Nigeria is scrambling for a solution to allow displaced people to vote, but Wase said any successful future attack on Maiduguri would “automatically disrupt the elections.”

“It means elections will not be held in Borno state because the bulk of the voters are now in Maiduguri,” he added.

Nigeria’s main opposition, which is in power in much of the northeast, has said the validity of the overall result could be questioned if hundreds of thousands of people are disenfranchised.