US and Iraqi forces are carrying out a major security operation in the northern city of Kirkuk, where a 12-hour curfew was imposed.

Iraqi police said that so far more than 20 suspects had been detained.

They said more then 3,500 Iraqi forces and hundreds of US soldiers were targeting al-Qaeda in Iraq militants.

Correspondents say there are rumours senior Al Qaeda activists may have made their way to Kirkuk to elude the surge in security in and around Baghdad.