Suspected Islamist insurgents overran the northeast Nigerian town of Dikwa in Borno state, a military stronghold and humanitarian hub, security sources, residents and an aid worker said on Tuesday.

Dikwa, which an army spokesman denied had been captured, is home to almost 100,000 people and has been a flashpoint town in the 11-year insurgency waged by jihadist group Boko Haram and its offshoot Islamic State West Africa Province.

“We tried our best to repel the attack but they already overpowered us,” said a soldier, describing the fighting he said began on Monday evening, underscoring a worsening security situation in the country’s north.

“We fled to the bush despite reinforcements from the air force,” said the soldier, declining to be named as he was not authorised to speak to media.

A second member of the military confirmed the town’s seizure, as did two Nigerian and two international security sources, four residents and an aid worker.

In a statement, an Army spokesman said it had repelled an attack on Dikwa, and called reports that insurgents had trapped aid workers “false and sensational.”

A spokesman for the governor of Borno did not respond to phone calls seeking comment.

Dikwa is one of the military’s “super camps” - towns repurposed as defensive strongholds in 2019 to help curtail a climbing military death toll, while ceding control of much of the countryside.

Nigeria’s security forces had pushed the insurgents out of the northeast’s major towns in 2015 and 2016, but now face a raft of security challenges across the country’s increasingly restive northern states.

Militants last week rained rocket-propelled grenades on the northeast’s biggest city, Maiduguri, while marauding armed gangs in the northwest who kidnap for ransom have abducted more than 600 school pupils in the last three months, including 279 girls who were freed on Tuesday.

No super camp had fallen until Marte in January this year, which was recaptured last week.

Residents in Dikwa said the attackers wore military uniforms and proclaimed themselves “soldiers of the Khalifa”, the term used by Islamic State’s West African branch.

No group has claimed responsibility for the attack on the town, which, like many super camps, doubles as a protected hub for populations displaced by the conflict, where humanitarian groups build camps and distribute food and supplies.

The fighters gathered residents together and preached that they were against the military and anti-Islam forces, three residents said.

The insurgents also burned or damaged the premises of aid agencies and a hospital, said a Nigerian security source and Edward Kallon, the United Nations’ Nigeria representative, citing reports.

“I am gravely preoccupied by reports of an ongoing violent attack by non-state armed groups in Dikwa,” Kallon said in a statement. “I strongly condemn the attack and am deeply concerned about the safety and security of civilians.”