Lagos - Amnesty International on Thursday urged Nigeria's government to criminalise torture, as it published a new report documenting widespread abuses in the criminal justice system and military.
The London-based rights group's report, "'Welcome to hell fire, Torture and Other Ill-treatment in Nigeria", catalogues the testimony of hundreds of victims compiled over the last 10 years.
"This goes far beyond the appalling torture and killing of suspected Boko Haram members," Amnesty's research and advocacy director, Netsanet Belay, said in a separate statement.
"Across the country, the scope and severity of torture inflicted on Nigeria's women, men and children by the authorities supposed to protect them is shocking even to the most hardened human rights observer.
"Torture is not even a criminal offence in Nigeria. The country's parliament must immediately take this long overdue step and pass a law criminalising torture. There is no excuse for further delay."
Nigeria has faced long-standing accusations of institutionalised abuses and in May this year Amnesty named the country as one of five worldwide where routine torture was of particular concern.
But there is little evidence that the problem has been tackled seriously, despite Nigeria being a signatory to seven regional and global agreements and its own constitution banning the practice.
In February 2012, Nigeria's then police chief, Mohammed Abubakar, admitted that the force had carried out extra-judicial killings and detained innocent people.
"Justice has been perverted, people's rights denied, innocent souls committed to prison, torture and extra-judicial killings perpetrated," he said in an address to senior officers.
Anti-robbery squads had become "killer teams" while corruption-ridden officers had lost the trust and confidence of the public "to do any good thing", he added.Also read: Church collapse: Nigeria search mission continuing - Zuma
- 'Medieval' practices -
Nigeria's police have since introduced a human rights course at training colleges for new recruits, Abubakar has said, but Amnesty's report lays bare the scale of the issue.
Amnesty said it had identified 12 commonplace torture methods, including beatings and shootings, suspending detainees upside down by their feet, starvation, sitting on sharp objects and choking.
Detainees were regularly held incommunicado while some police stations have an "officer in charge of torture", meting out treatment from electric shocks and sexual violence to nail and teeth extractions to elicit confessions and information.
Some 500 allegations of torture have been documented as a result of interviews with victims, their families, lawyers and rights defenders since 2007, Amnesty said.
The group and others have previously highlighted the alleged abuse of suspected Boko Haram members detained in inhumane conditions in military facilities in the restive northeast.
Children under 18 have been among the thousands held since the violence began in 2009, with many picked up on the flimsiest evidence.
Belay said their treatment and the so-called "screening" process resembled "a medieval witch-hunt".
Lack of accountability has allowed an institutionalised culture of abuse to go unchecked, the group added, echoing previous comments from United Nations' representatives on human rights and torture as far back as 2005.
A bill to outlaw torture has been held up in parliament for the last two years.
"Our message to the Nigerian authorities today is clear -- criminalise torture, end incommunicado detention and fully investigate allegations of abuse," said Belay.
"That would be an important first step towards ending this abhorrent practice. It's high time the Nigerian authorities show they can be taken seriously on this issue."