Gunmen suspected to be Islamist militants have shot 44 people praying at a mosque in Konduga, some 35 kilometres outside Maiduguri, Borno state, according to report.
The killings reportedly took place during prayers on Sunday morning, although news only emerged on Monday.

Men dressed in military camouflage arrived in Konduga town on Sunday morning and shot or hacked to death dozens of people returning from morning Muslim prayers, two residents said.

"They took everybody by surprise with the attack," a military joint task force source told Reuters, asking not to be named. "They killed many people, the victims are more than 30 but I cannot confirm the exact number."

A hospital source told news reporters that 26 wounded people were receiving treatment after the attack in Konduga, a small town around 25 km (15 miles) from Maiduguri, the capital of Borno state.

Boko Haram, which wants to impose sharia law in Nigeria's north, and other spin-off Islamist groups have become the biggest threat to stability in Africa's top oil exporter.

In mid-May, President Goodluck Jonathan declared a state of emergency and launched an offensive against the group in its stronghold in the northeast. The insurgency was initially weakened but remains active, and guerrilla-style attacks persist.

The group's leader, Abubakar Shekau, said in a video distributed to journalists on Monday that his fighters had carried out several attacks in Borno state in recent weeks where "soldiers fled under our heavy firepower".

"We have killed countless soldiers and we are going to kill more. Our strength and firepower has surpassed that of Nigeria. We can now comfortably confront the United States of America," he boasted in the local Hausa language.

Civilian vigilante groups have sprung up to help Nigerian forces identify and arrest Boko Haram members, but there are concerns among security experts that the spread of vigilantes could further erode law and order.