LAGOS (Reuters) - Torture is so common in Nigeria's police force that many police stations have a designated officer to carry out atrocities such as pulling teeth, choking, raping and delivering electric shocks to detainees, Amnesty International said on Thursday.

In a report entitled "Welcome to Hellfire", the human rights organisation said police routinely used torture to extort cash or extract confessions from suspects, even some as young as 12.

Doing so does not even break the law, Amnesty said, as Nigeria has yet to pass legislation criminalising torture.

Nigeria's police spokesman Emmanuel Ojukwu dismissed the report as containing "blatant falsehoods and innuendoes", and said Amnesty had made no efforts to speak to police authorities.

"Torture or ill-treatment is not, repeat, not an official policy of the Nigeria police," he said.

Some alleged abuses were linked to the five-year insurgency in the country's north-east by Boko Haram militants, but Amnesty said they were by no means restricted to it, as torture was practiced throughout the nation of 170 million people.

"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 to even the most hardened human rights observer," Netsanet Belay, research director at the rights group, said in a statement.

Amnesty interviewed some 500 survivors of torture, from whom they heard tales of beatings with iron rods and the rape of a 24-year-old woman who had tear gas sprayed into her vagina.

Common torture methods included beatings of detainees with rifle butts, rods and cables while suspended with a rope, nail and tooth extractions, starvation, sitting on sharp nails and throwing hot water on wounds, Amnesty said.

Nigeria's security forces are often accused of brutality and graft, but Amnesty's report carries much detail on the kinds of atrocities it says they have committed in the past decade.

While rejecting the findings, Ojukwu said: "the Nigeria Police Force shall meticulously scan through the document, and investigate any current human rights abuses linked to any officer or formation".