Britain's police watchdog has launched an investigation into claims that six London officers used torture methods, including a variation of "waterboarding", on suspects arrested in drug raids.
The Independent Police Complaints Commission (IPCC) said on Wednesday it was investigating "the conduct and actions of six police officers during the execution of two drugs warrants at addresses in north London on November 4, 2008".
The probe was launched after UK national newspapers reported the officers had allegedly used brutal techniques, including forcing suspects' heads into buckets of water to induce the sensation of being drowned.
London's Metropolitan Police force confirmed the six officers were suspended over their conduct during the arrests of five people in the London borough of Enfield.
The force would not comment on the nature of the allegations.
Boris Johnson, London's mayor, said the allegations were "extremely serious and need to be thoroughly investigated".
Two newspapers, The Times and the Daily Mail, and Britain's Sky News television channel reported that officers had allegedly held suspects' heads under water.
The Metropolitan Police said a police employee had raised concerns about "a small number of officers" in Enfield, and the case had been referred to the watchdog in April.
The force said that, if allegations of wrongdoing were proved true, "the strongest possible action will be taken".
Britain is signatory to the United Nations Convention Against Torture, which requires that governments prevent torture anywhere under their jurisdiction.
London police officers are also facing allegations that they used excessive force during protests against the G20 summit in London in April.
The IPCC is investigating several incidents, including the death of Ian Tomlinson, a newspaper vendor, who collapsed and later died after he was pushed to the ground by police.
Results of an initial autopsy suggested Tomlinson died of a heart attack, but a second examination said he had suffered internal bleeding.