In a report published Wednesday, the London-based rights group accused Nigerian police of rampant human rights violations, including extra-judicial killings, torture and enforced disappearances.
Amnesty International has released a new report saying Nigerian police are responsible for hundreds of unlawful killings every year.
Under Nigerian law police officers are allowed to shoot suspects and detainees who try to escape or avoid arrest. Amnesty International says this law gives the police permission to shoot at will.
According to official Nigeria police force statistics 857 armed robbers were killed and 53 were injured in 2008. The police publish such information, says Amnesty International Nigeria campaigner Lucy Freeman, to show that they're doing a good job at fighting crime.
"So it's more than just individual people and individual officers who are not following the law. This is becoming something of a tool of policing we fear," she said.
Amnesty International says the majority of unlawful police killings in Nigeria are not investigated and the victims' families receive no justice.
And it says in some cases unarmed and innocent people are killed by police, who later accuse the dead of armed banditry.
Freeman says in violence-rife Nigeria, there is much public support for the crackdown on banditry.
"Unfortunately there's some public support for very harsh treatment of armed robbers and some public support for torture and for execution of them. There's very little outcry when a so-called armed robber or a so-called kidnapper is killed by the police," she said.
But Nigeria police force spokesman Manuel Ojukwu says the Amnesty Report is unbalanced. He says police killings are always investigated.
"There are laws guiding such use of firearms and anybody who kills anybody in the course of duty must explain and justify his action," he said.
And he says the report has failed to portray the high number of police deaths. He says this year over 300 police officers have been killed.
"In the course of police operations many officers have also lost their lives -- Amnesty did not reflect that," he said.
But he adds the police force is facing challenges, which, with government funding, should be overcome.
The Nigerian police force is severely underfunded - many officers do not have basic equipment, such as bulletproof vests or handcuffs.
Amnesty International's report, "Killing at Will", is the result of three years of research between 2007 and 2009.