Lagos, Nigeria (CNN) -- Police corruption and abuse are rife in Nigeria, Africa's most populous nation, according to a report from Human Rights Watch.
The New York-based group issued a 102-page report Tuesday saying that "widespread corruption in the Nigeria Police Force is fueling abuses against ordinary citizens and severely undermining the rule of law in Nigeria."
"Good policing is the bedrock for the rule of law and public safety," said Corinne Dufka, senior West Africa researcher at Human Rights Watch. "The long-term failure of the Nigerian authorities to address police bribery, extortion, and wholesale embezzlement threatens the basic rights of all Nigerians."
Agence France-Presse quoted police spokesman Emmanuel Ojukwu as saying the report "contains largely embellished innuendos ... aimed at reaching a preconceived conclusion."
"The Nigeria Police Force has come a long way from its colonial era of oppression and has survived many years of neglect and under-funding," Ojukwu is quoted as saying.
Human Rights Watch said the report reflects "the myriad forms of police corruption in Nigeria" and "also shows how institutionalized extortion, a profound lack of political will to reform the force, and impunity combine to make police corruption a deeply embedded problem."
The study was based on interviews with more than 145 victims of and witnesses to police corruption in Nigeria. Among them are "market traders, commercial drivers, sex workers, criminal suspects, and victims of common crimes; rank-and-file and senior-level police officers; federal government officials; judges, prosecutors, and lawyers; religious and civil society leaders; journalists; diplomats; and members of an armed vigilante group."
The report focuses on extortion and bribery, embezzlement, and failures of oversight.
One corrupt practice detailed in the findings is called "returns" -- "in which rank-and-file officers are compelled to pay up the chain of command a share of the money they extort from the public." Another form of corruption the report noted is the practice of forcing crime victims "to pay the police to conduct every stage of an investigation."
"Those with no means to pay are left without justice, while criminal suspects with money can simply bribe the police to drop a case, influence the outcome of a criminal investigation, or even turn the case against the victim," Human Rights Watch said.
"Justice is for sale to the highest bidder," the report quoted one activist as saying.