Royal Military Police have arrested a man in connection with video footage of British troops allegedly abusing Iraqi civilians.
He was detained last night, but officials refused to say where or confirm if he was a serving soldier.
The images released by the News of the World, taken in southern Iraq two years ago, show troops kicking, punching and striking young civilians with batons, while a colleague filming the footage is heard laughing.
Cameraman in British troops abuse video
Iraqi prime minister Ibrahim al-Jaafari has called for a rapid investigation into the footage.
Dr Bashar Al Naher, a UK-based spokesman for the Iraqi prime minister, urged Prime Minister Tony Blair to bring the perpetrators to justice immediately.
Mr Blair promised a thorough investigation into the incident which is being broadcast to outrage across the Middle East.
Arab satellite television stations, including Al-Jazeera and Al-Arabiya, are replaying the footage alongside images from the Abu Ghraib prisoner abuse scandal involving US soldiers.
"We take seriously any allegations of mistreatment, and those will be investigated very fully indeed," Mr Blair said.
The soldiers are shown apparently dragging four youths into an army compound from Basra streets, where groups of young Iraqis had been throwing stones at soldiers.
The cameraman is heard laughing and saying: "Oh yes! Oh yes! You're gonna get it. Yes, naughty little boys. You little f***ers, you little f***ers. Die. Ha Ha."
The News of the Worldsaid the 2004 tape was shown at the troops' home base in Europe before being handed over by a whistleblower.