The arrested police officers, who appeared on the tape, were apprehended in Maiduguri, the capital of the northern state of Borno, according to the Al Jazeera website.

The Arabic news agency reported: "We understand that their arrests were ordered by the inspector general of police and that police in the state are still looking for officers who may have been involved in those killings.

"This comes after the federal government decided to launch an investigation into that exclusive report. They ordered the inspector general of police to investigate what happened.”

An estimated 1,000 people were killed as Nigerian government forces fought Boko Haram in Borno, Yobe, Kano and Bauchi states in July and August of 2009. But the footage obtained by Al Jazeera shows that many of the deaths occurred only after the fighting was over.

The Nigerian House of Representative have also constituted a committee to probe into the issue.

But Nigerian officials have since acknowledged that extra-judicial killings took place and an inquiry was set up to investigate the incident. Among those killed in the aftermath of the clashes between Boko Haram and the police, was Boko Haram leader Mohammed Yusuf.

Based on the footage in the custody of the news network, he is seen wearing handcuffs and surrounded by heavily armed police officers. Nigerian police have said that Yusuf was killed while attempting to escape, but he died still wearing the handcuffs.