A new Amnesty International report says an elite Nigerian police squad set up to combat violent crime is torturing detainees to extract lucrative bribes and confessions.

The report says the Special Anti-Robbery Squad demands bribes, steals and extorts money from criminal suspects and their families and is "fomenting a toxic climate of fear and corruption."

Police spokesman Deputy Commissioner Donald Awunah did not respond to requests for comment. London-based Amnesty says its questions met with a police denial that any torture occurs.

The report says many officers bribe police chiefs to get onto the special squad where "torture is a lucrative business."

Nigeria's President Muhammadu Buhari promised to stamp out endemic corruption when he won elections in March 2015, but it is proving an uphill battle.