“There have been huge explosions and sporadic gunfire around (the) Shagari Low Cost area of the city,” said Gbadegesin Toyin, police spokesman in Yobe state of which Damaturu is the capital.

“We still don’t have details of what is going on but we have alerted our men to confront any eventuality,” he said.

Damaturu, which is near Boko Haram’s base of Maiduguri, is under curfew, with residents forced to be in their homes from dusk to dawn following running clashes between troops and Islamists last month.

A resident of the affected area, Babagana Abdullahi, told AFP earlier that his neighbourhood had been “besieged by loud explosions and shootings,” and that he could not tell what was happening because he was confined to his home due to the curfew.

Contacted again, he said, “the explosions and shootings have stopped in the last twenty minutes but they lasted two hours.”  Nigeria’s radical Islamists have repeatedly attacked the city, typically targeting the security services, while a specialised army unit has initiated raids on suspected Boko Haram hideouts.

One such raid occurred last Saturday, when the Joint Task Force (unit) said it received intelligence about an impending Boko Haram attack and launched a pre-emptive offensive that left three of the sect members dead.

The group rents residential homes in the city, converts them into arms depots and then uses the buildings to plan raids, according to security sources.

Boko Haram’s attacks in the area have previously hit police stations as well as prisons, where the Islamists say their leaders are being illegally detained.

The group has said it wants to create an Islamic state in northern Nigeria, although its demands have varied widely since it renewed its insurgency in 2010.

The city was shut down by fierce fighting last month after suspected Boko Haram gunmen launched coordinated gun assaults on several targets after learning that one of their senior operatives had been arrested.

The resulting clashes killed at least 40 people, led the Yobe state government to impose a city-wide ban on movement, which temporarily stranded residents unable to return home or access food.

Nigeria has been criticised for what some term the heavy-handed raids on alleged Boko Haram targets, while doing little to temper the Islamist threat.

Three of Boko Haram’s leaders were last month designated global terrorists by the US State Department, which said the group was responsible for more than 1,000 deaths since the start of last year.

Nigeria, Africa’s most populous country and the world’s eighth largest oil producer, is roughly divided between a predominantly Muslim north and a southern, wealthier half, where most are Christian.