ABUJA: Aid groups in Nigeria said Wednesday six civilians died in a suspected jihadist attack on a northeastern town that, according to the UN, "directly targeted" aid facilities.

"At least six civilians lost their lives in crossfire, several others were injured and are still missing," the Nigeria INGO Forum, gathering 54 international charities, said in a statement.

A military source told AFP that fighters from the Islamic State West Africa Province (ISWAP), which split from mainstream Boko Haram in 2016, were behind an assault on the town of Dikwa that began late on Monday.

"ISWAP terrorists launched simultaneous attacks on the super camp (military base) and the UN humanitarian hub," the source said.

The hub is one of nine in northeast Nigeria where aid workers live and work.

A spokesperson for the International Committee of the Red Cross (ICRC) in Nigeria told AFP it had received six injured people for treatment.

The UN's humanitarian coordinator in Nigeria, Edward Kallon, said on Tuesday the insurgents had "directly targeted" aid facilities, affecting efforts to help nearly 100,000 people in need.

The Nigeria INGO Forum said "the full scale of the attack's impact on civilians... is still being assessed."

The Nigerian army said it had it "repelled" the attackers.

"The terrorist groups who stormed the town in an unconfirmed number of gun trucks and motorcycles were visited with heavy bombardment and overwhelming firepower," army spokesman Mohammed Yerima said in a statement on Tuesday.

But three sources who requested anonymity told AFP that the insurgents were able to take the town for several hours between Monday evening and mid-day Tuesday.

The army or the government have not released an official death toll.

Dikwa is home to nearly 114,000 people including 75,470 internally displaced persons (IDPs) -- people living in Nigeria who have fled their homes because of conflict.

President Muhammadu Buhari reshuffled the military command this year, raising hopes of a shift in strategy to end a 12-year-old conflict that has killed 36,000 people and forced around two million to flee their homes.

Since 2019, three humanitarian hubs - Banki, Ngala and Monguno -- have been targeted in attacks by insurgents.

Due to worsening security, humanitarian workers in Nigeria are struggling to provide aid.

The UN estimates that 8.7 million people will require urgent assistance this year.