Iraqi security forces have begun preparing for a huge operation to hunt down insurgents in the Baghdad area.
Troops will search Baghdad district by district
The first of an estimated 40,000 soldiers and police involved have been setting up checkpoints, in an effort to seal roads in and out of the capital.
Operation Lightning follows an upsurge in insurgent attacks, which have killed more than 600 in the past month.
Rebels continued their attacks on Sunday, killing nine troops in south Baghdad and a UK soldier near Amara.
Civilians were also killed as violence continued in and around Baghdad, despite the launch of the anti-insurgency operation.
- Three people were killed and 20 injured by a car bomb targeting police in western Baghdad
- Two people died and six were hurt in a suicide car bombing near Baghdad's oil ministry
- Two police officers were killed by a car bomb explosion in Madain, south-east of the capital
More attacks expected
Iraq's defence and interior ministers announced last week that Operation Lightning would involve Iraqi forces searching Baghdad district by district, looking for insurgents, foreign fighters and weapons caches.
They said it would be the largest Iraqi military operation since the fall of Saddam Hussein.
"The troops will block all entrances of Baghdad to prevent terrorists from conducting activities in the capital," a defence ministry official was quoted as saying by Reuters news agency.
"It's a crackdown on the terrorism infrastructure."
Vehicles were searched and roadblocks were set up across the city. Some buildings were also raided.
The operation is to be backed by 10,000 US troops based in the area.
A spokesman for Iraqi Prime Minister Ibrahim Jaafari said the government expected insurgents to challenge the offensive by trying to launch more attacks.
"With the escalating operations by security forces, we expect such reactions coming to the surface, but this will have no effect on the operations," he said during a news conference.