Britain is to head an international force of more than 16,000 troops to enhance security and peacekeeping operations in southern Iraq, it emerged on Tuesday.
The move, which is expected to be announced in the UK parliament this week, is part of a substantial deployment of extra troops to Iraq and comes as tensions throughout the country continue to rise.
The plan for an international peacekeeping force has been pushed by the US which is desperate to take the pressure off its forces in Iraq.
It is also a tacit recognition that British and US forces need reinforcements to maintain order.
Britain already has 11,000 troops in the south of the country. According to British and US defense sources, they will be supplemented by more than 5,000 soldiers from Denmark, the Czech Republic, the Netherlands, Italy, Norway, Portugal, Romania, New Zealand and Lithuania.
A second international force, deployed elsewhere in Iraq, is expected to be led by Poland.
There were reports on Tuesday that a third peacekeeping force will be established, possibly led by India.
General Richard Myers, chairman of the US joint chiefs of staff, said on Tuesday that up to 20,000 foreign troops were "gearing up" to go to Iraq.
"The flow would start in July or August and probably finish in September," he said.
Paul Bremer, the US administrator in Iraq, said on Tuesday that evidence from captured or killed assailants showed professional commandos from former president Saddam Hussein's old power structure were behind recent attacks on occupying forces.
"They're on the losing side of history," he said.
The majority of attacks on US soldiers have come in the "Sunni triangle" north and west of Baghdad, where Operation Sidewinder is concentrating, and the town Fallujah, 55km west of Baghdad, has been a particular hotbed of anti-American activity and the scene of many skirmishes with US soldiers.