Nigeria's military sent reinforcements Friday to the remote northeastern town of Benisheik after Boko Haram Islamists stormed the area, burnt dozens of homes and slaughtered at least 87 people.

The Islamist insurgents were heavily armed and came disguised in military uniforms during the attack late Tuesday, according to survivors and security sources.

They set up roadblocks and opened fire on scores of motorists and travellers who had tried to pass through, leaving some corpses scattered on the roadside after the assault.

The motive for the attack was not immediately clear, but Boko Haram has repeatedly targeted civilians in its four-year insurgency, which the group says is aimed at creating an Islamic state in northern Nigeria.

Army General Mohammed Yusuf told journalists who visited the area that a "full reinforcement" of Benisheik would take place Friday.

A state government official, who requested anonymity, told AFP Friday that those troops were being sent, but details of the deployment were not immediately available.

Benisheik in Borno state has emerged as a new flashpoint in the Boko Haram conflict, with Tuesday's massacre coming after September 8 clashes between Islamists and vigilantes that left 18 people dead.

The extremists have in recent weeks repeatedly targeted vigilante groups which have formed to assist the military.

Saidu Yakubu of Borno's Environmental Protection Agency told journalists who visited the town Thursday that 87 bodies had been discovered after the massacre, but that toll could rise.

An official with the same agency, Abdulaziz Kolomi, told reporters that rescue teams "did not go deep into the bush" in their search for victims.

"I strongly believe many people have fallen there," he said, raising the possibility that more bodies could still be found.

The phone network in Borno has been turned off since mid-May, a tactic the military employed to disrupt communication between the insurgents.

Some have charged that the lack of mobile phones has put civilians at risk because they are unable to call for help amid Boko Haram raids.

Details of attacks have also been difficult to verify with the phone network down.

A security source in Benisheik who asked for anonymity told journalists that the Islamists were armed with "anti-aircraft guns".

He said "they came in droves, driving about 20 pickup trucks" and forced the soldiers to retreat.

Such details are consistent with other reports indicating that Boko Haram has bolstered its arsenal in recent months.

Speaking to AFP Friday, army spokesman Ibrahim Attahiru said "the police were overwhelmed by the attack", but did not comment on reports that military personnel ran out of ammunition and were forced to abandon Benisheik as the insurgents attacked.

The military has insisted that a four-month-old offensive in the northeast has put Boko Haram in disarray, but the recent spate of violence suggests otherwise.

Local media this week reported that Boko Haram had ambushed a group of soldiers, killing 40 with dozens of others missing, although the military disputed that account.

Attacks on defenceless civilians have spiked in recent weeks, including the massacre of dozens of school children and Muslims gathering for morning prayers.

Throughout their four-year insurgency, the Islamists have bombed churches, newspaper offices, a United Nations building and prominent mosques, among other targets.

The conflict is estimated to have killed more than 3,600 people since 2009, including deaths caused by the security forces, who have been accused of major abuses.

But the current toll is likely much higher and the violence has persisted, despite the renewed military efforts.

Nigeria is Africa's most populous country and top oil producer, where the south is mostly Christian and the north, where poverty is most acute, is mainly Muslim.