British and Iraqi forces have launched a major drive in Basra city aimed at purging the police of the militias that have infiltrated their ranks.
Parts of the police force have been taken over by militias
About 1,000 British troops and 2,300 Iraqis have begun to deploy as part of what the Army labels Operation Sinbad.
The UK military said the operation, to last until February 2007, was intended to prepare for the expected handover of power to Iraqi officials next year.
Shia militias have effectively seized control of the police in some areas.
Operation Sinbad will see small "transition teams" of Royal Military Police being inserted into police stations throughout the southern Iraqi city for 30 days at a time.
Major Charlie Burbridge, spokesman for the Army in Iraq, described it as a "big push to take Basra as close as we can to transition to Iraqi control".
"We have to accept that elements of the police have been infiltrated by elements of the Shia militia," he said.
"Part of this will involve us identifying those policemen who are unable or unwilling to do their duty as policemen.
"Those who are particularly bad are likely not to be policemen for much longer."
Shia militias have infiltrated the police since 2005, enabling them to impose control on parts of the city.
Operation Sinbad will also include a renewed reconstruction effort, redeveloping hospitals and distributing educational material to the city's schools.