Nigerian soldiers have reportedly killed 16 men in the country's northeast just hours after they were arrested leaving a mosque, according to nurses at a hospital that received the bodies.

Troops rounded up 17 people, including a Muslim religious leader, as they left morning prayers at a mosque on Wednesday from the Dogo Tebo area of Potiskum in Yobe state.

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Residents and hospital staff said the bodies of 16 men were found dead with bullet wounds. 

"All the bodies have gunshot wounds on them," a nurse speaking on condition of anonymity said.

Residents said the Muslim religious leader was not among the dead, and said they were "worried about what they could do to him".

Community leaders believe the 16 men were picked up and killed because all of them were from the Kanuri ethnic group that forms the bulk of Boko Haram's membership.

"We demand a probe into this unjustifiable murder," said one community leader, adding "our fear is we don't know what they will do next".

Extra-judicial killings

Human rights groups in Nigeria and abroad have previously accused the military of carrying out extra-judicial killings in the fight against Boko Haram.

Amnesty International, the UK-based rights monitor, said in March that there was "credible evidence" that more than 600 people were summarily executed in the Borno state capital, Maiduguri, after a Boko Haram jail break.

Who are Nigeria's Boko Haram?

Concerns have also been expressed about atrocities perpetrated by vigilantes, who have assisted the military against Boko Haram.

On Friday vigilantes in the Borno town of Biu said they and troops had decapitated 41 Boko Haram fighters who were planning a raid in the village of Sabon Gari, in the south of the state.

Two residents said the heads were put on spikes and paraded through the town.

"It was like hunters displaying their game after a hunting expedition," Silas Buba, a resident, said.

Human Rights Watch, the US-based rights monitor, said the alleged beheadings were consistent with the vigilantes' recent conduct.

Formed in 2002, Boko Haram is against Western education and has been battling the government in the country's north and has repeatedly attacked schools, churches, mosques and markets as it seeks to impose a strict interpretation of Islam in territory it controls.

More than 700,000 people have been displaced externally and internally as government forces try to hunt down Boko haram fighters, the UN refugee agency, UNHCR says.

Source: Al Jazeera and agencies