Iraqi police have detained 527 suspects in Baghdad, according to sources in the Interior Ministry.
They are suspected of involvement in a number of different crimes. The source said the raids had begun in the early hours and were still under way.
Elsewhere, Kurdish and US forces arrested 15 members of a militant group accused by Washington of links to al-Qaeda in raids in three Iraqi cities, a senior Kurdish official said today.
One of those arrested during the joint operation yesterday was suspected to be a senior figure in Ansar al-Islam, a group accused by Iraq's interim government of carrying out attacks in Iraq, the official said.
The official, from the Patriotic Union of Kurdistan party - which controls a swathe of territory in northern Iraq - said the raids took place in Kirkuk, Samarra and Baquba, all north of Baghdad.
The Kurdish official said security forces were trying to ascertain whether one of the suspects arrested was Heymen Dani-Shari, suspected to be one of the top leaders of Ansar al-Islam in Iraq.
The US military said it had no information on the arrests.