The leader of Boko Haram has claimed responsibility for the recent brutal massacre in Baga in northeast Nigeria and has threatened more violence, saying "We will not stop".

In a 35-minute video obtained by AFP news agency, a man purporting to be Abubakar Shekau boasts of the attack on 7 January which killed hundreds of people. Witnesses reported that as many as 2,000 people were killed when insurgents attacked the town in Borno state four days after overrunning a nearby military base, though the Nigerian government refutes this claim, putting the figure at just 150.

"We killed the people of Baga. We indeed killed them, as our Lord instructed us in His Book," Shekau said in his latest video.

"We will not stop. This is not much. You'll see."

Shekau is seen standing in front of several vehicles, flanked by a number of masked, heavily armed men. The Nigerian army has in the past claimed to have killed the militant leader, but each time Boko Haram has released a video in which Shekau – or possibly a lookalike – declares that he remains alive and in charge.

He promised his followers are ready to take on anyone trying to stop them. "The kings of Africa, you are late. I challenge you to attack me even now. I'm ready," he said.

Bishop Oliver Dashe Doeme of Maidguri, the capital of Borno, this week called for the West to send in military troops to "crush" Boko Haram.

"The West should bring in security – land forces to contain and beat back Boko Haram. A concerted military campaign is needed by the West to crush Boko Haram," the bishop said in an interview with Aid to the Church in Need.

He added that 50 churches in his diocese have been destroyed by militants in the past five years, and over 1,000 congregants have been killed, some of them because they refused to convert to Islam. Over half of the Catholics in Maidguri have fled their homes since 2009 – a figure estimated at around 70,000.

"The threat we face presents a very bleak future for the Church. Many of our members are scattered and others have been killed. In some areas there are no Christians anymore," Bishop Dashe Doeme said.

"But the Church belongs to Christ. The Church will remain strong and many of our people have returned after land has been taken back by the Nigerian soldiers."