"An investigation proved these people were not linked to Ansar al-Islam," said Saif al-Din Ali Ahmed, chief of public security in northern Iraq.

A violent Islamist movement with alleged links to Al-Qaeda, the outlawed Ansar al-Islam, based in the autonomous Kurdish region, has been attacked by US forces and is accused of taking part in the insurgency raging in Iraq.

Ahmed said Kurdish security forces rounded up a total of 15 Islamists in a sweep in late December, six of whom were still being investigated.

Kamel Haji Ali, a member of Al-Haraka Al-Islamiya, said at the time that dozens of activists from both his movement and Al-Jamaa Al-Islamiya, were rounded up in Halabja, near the Iranian border northeast of Baghdad.

The two parties targeted in the arrests are tolerated in Iraq.