Ansar al-Islam ("Supporters of Islam") was formed in December 2001, one of numerous small splinter factions in the region of northern Iraq that is controlled by ethnic Kurds, according to U.S. officials.
It has several hundred members and broke away from another group, Jun al-Islam, which itself was formed in September 2001.
It is composed primarily of Kurds -- and some Arabs -- who follow an extremist brand of Sunni Islam, but their focus is primarily opposing the Patriotic Union of Kurdistan, one of two large secular Kurdish groups that oppose Saddam Hussein with U.S. support.
Led by Mullah Najm al-Din Faraj Ahmad, Ansar al-Islam operates in PUK territory around Halabjah, Iraq, which is close to the border with Iran. It has some presence in the village of Biyara.
Some U.S. officials say the group also opposes Saddam Hussein's government, which killed thousands of Kurds with chemical weapons in that region in the 1980s.
The group operates well outside of Saddam's sphere of influence, although other U.S. officials believe Saddam also tacitly or directly supports the group to make trouble for the PUK.
About a dozen members of Ansar al-Islam trained in camps in Afghanistan in 1999 and 2000 and had contact with members of Usama bin Laden's Al Qaeda organization. As Arab members of Al Qaeda have been fleeing overland from Afghanistan through Iraq, some have been given shelter by Ansar al-Islam members.