U.S. and Iraqi forces have detained six members of a militant group suspected of carrying out a series of assassinations in the country's northern region, Iraqi police said Sunday.

The men reportedly belong to Ansar al-Islam (search), a Kurdish group believed linked to al-Qaida. They were arrested in a midnight raid on a house in the Oruba district of Kirkuk. Five are Iraqi Arabs while the sixth is a Kurd, said Col. Sarhat Qader, a police official.

"Two of the men were from Ramadi while three were from Kirkuk," Qader said.

Ramadi (search), a city in the so-called Sunni Triangle, has been the site of frequent clashes between U.S. forces and insurgents, some of whom are Saddam Hussein supporters.

Kirkuk, which sits atop vast northern oil reserves, is an ethnically diverse city whose residents include Arabs, Kurds and Turkomen. The city has seen a string of assassinations and attacks on senior police and political leaders.

Last month three top officials, including Ghazi Talabani, the head of security for the state-run Northern Oil Company (search), were killed in ambushes by masked gunmen. Talabani was also the cousin of Jalal Talabani, the leader of one of the two main Kurdish political parties, the Patriotic Union of Kurdistan.

Gunmen also killed an Education Ministry official and a deputy foreign minister.

Iraqi officials, along with officials from the now-defunct coalition authority, had worked to mollify sectarian tensions in the city.