Updated

Suspected Boko Haram Islamists have stormed a town in northeast Nigeria, opened fire on police and civilians and killed 11 people, residents and a local lawmaker told AFP Friday.

The attack happened late Thursday in the town of Damboa in Borno state, Boko Haram's stronghold and where Nigeria has imposed a state of emergency as it pursues an offensive against the insurgent group.

"The attack lasted until about midnight," said Adamu Isah, a student who lives in Damboa. He said groups of gunmen opened fire on police and civilians and that "11 people died."

He blamed the attack on "Boko Haram" fighters.

State lawmaker Ayamu Lawan Gwasha, who represents Damboa, confirmed the details, as did a local security official who requested anonymity.

Both Isah and the lawmaker spoke to reporters in Borno's capital Maiduguri, roughly 85 kilometres (52 miles) from Damboa. Both said they had fled to the capital after the attack.

Details were slow to emerge and the area military spokesman could not be reached for comment because of a phone blackout imposed by the military, an operational measure meant to block the Islamists from coordinating attacks.

The phones have been down in Borno since May, when the state of emergency was declared.

The lawmaker said the town had been on high alert since the weekend, when 47 people were killed in the town of Konduga, also in Borno state, in a brutal attack that targeted Muslim worshippers gathering for morning prayers.

"We raised the alarm" after Konduga, Gwasha told journalists, saying the heightened security presence in Damboa "has helped in reducing the magnitude of the attack."

The military has sought to portray Boko Haram as being on the defensive, claiming that the sweeping operation launched in May has plunged the extremists into disarray with all their camps destroyed.

But a spate of recent deadly violence has raised doubts about the military's claims. With the phone network down, information about the operation has been difficult to verify and access to the northeast is restricted.

Boko Haram has said it is fighting to create a strict Islamic state in northern Nigeria, but much of its violence has targeted Muslims.

It has also killed Christians and frequently targeted the security services as well as other symbols of authority.

Some speculate the group has sought out soft targets as it has faced added military pressure. A brutal attack on a school in northeastern Yobe state last month left 41 students dead.

But others counter that Boko Haram is simply demonstrating that it remains unhindered by the military assault, attacking a range of targets in different areas.

The insurgency is estimated to have claimed more than 3,600 lives since 2009, including killings by the security forces.

At bilateral security talks on Thursday, US Under Secretary of State for Political Affairs Wendy Sherman said a military crackdown alone would not end the conflict, calling instead for a plan to lift the mainly Muslim north out of extreme poverty.

The southern half of the country, Africa's most populous, is mainly Christian and considered wealthier than the north.