Al Jazeera's Yvonne Ndege, reporting from Abuja on Sunday, said the 17 police officers, who appeared on the tape, were apprehended in Maiduguri, the capital of the northern state of Borno.

"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," she said.

"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.

Political pressure

Our correspondent said members of Nigeria's House of Representatives who sit in the country's national assembly have also organised a committee to look into what happened.

IN DEPTH

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"The police have been under some political pressure to answer exactly what went wrong.

"However, there are some organisations who deal with things like extra-judicial killings who are concerned with the possibility that the government might be seeking to politicise that report on Al Jazeera."

In the video, a number of unarmed men are seen being made to lie down in the road outside a building before they are shot.

The family of Baba Fugu Mohammed, a respected community leader, told Al Jazeera earlier this month that he was among those put to death outside the police station.

Fugu Mohammed was the father-in-law of Mohammed Yusuf, the Boko Haram leader whose group had battled the police, but the two had become estranged.

His family said that he had come to help police restore order, but was shot.

Acknowledgment of killings

In the days following the clashes between the police and Boko Haram, the government, police and military repeatedly denied that civilians had been killed by their personnel.

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.

In the Al Jazeera footage, 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.

Boko Haram, which means "Western education is prohibited" in the local Hausa dialect, has called for the nationwide enforcement of a strict interpretation of Islamic law, or sharia, even among non-Muslims.

Last year's clashes took place after suspected Boko Haram members, armed with machetes, knives, bows and arrows, and home-made explosives, attacked police buildings and officers.

Nigeria's 150 million people are nearly evenly divided between Christians, who dominate the south, and the primarily northern-based Muslims.

Islamic law was implemented in 12 northern states after Nigeria returned to civilian rule in 1999 following years of military rule.