Now Nigeria's Jihadis Declare An 'Islamic Caliphate': Boko Haram Releases Video Proclamation That Shows Massacre Of Prisoners

Boko Haram's leader has declared an Islamic caliphate in a northeast Nigeria town seized by the extremist militants earlier this month.

Abubakar Shekau, the terrorist behind the kidnapping of more than 200 schoolgirls four months ago, made the statement during a video which shows a group of prisoners being shot with assault rifles as they lie in a ditch.

He declared that Gwoza, in Borno State, now has 'nothing to do with Nigeria' and said 'by the grace of Allah' they will not be leaving the town.

'Thanks be to Allah who gave victory to our brethren in (the town of) Gwoza and made it part of the Islamic caliphate,' he claims during the 52-minute video.

'By the grace of Allah we will not leave the town. We have come to stay,' said Shekau, who has been designated a global terrorist by the United States and sanctioned by the UN Security Council.

The United Nations humanitarian office (OCHA) earlier this month confirmed reports that Gwoza was under rebel control.

Boko Haram is also believed to be in control of other areas near the seized town in southern Borno, as well as large swathes of territory in the north of the region and at least one town in neighbouring Yobe state.

Mapping the precise areas which have fallen into Islamist hands is nearly impossible.

There are few humanitarian workers on the ground in the northeast, travel is dangerous and the region, which has been under a state of emergency since May of last year, has poor mobile phone coverage.

Experts have described Boko Haram's gains in recent weeks as unprecedented, saying the group was closer than ever to achieving its goal of carving out a strict Islamic state across northern Nigeria.

But many analysts believe the military has the capacity to reverse the insurgents' advance.

Soldiers this week refused to deploy to Gwoza without better weapons in an apparent mutiny.