Baghdad ? A suicide bomber attacked a meeting of pro-government Sunni sheiks west of Baghdad on Thursday, killing at least 23 people, including three U.S. Marines. At least 18 more people died in a car bombing in the northern city of Mosul.

Both attacks happened in Sunni Arab areas where al-Qaida in Iraq has been active. They appeared to be part of a campaign by both Sunni and Shiite extremists to undermine U.S. efforts to shore up local administrations and secure the security gains achieved since early last year.

The target of the Mosul blast appeared to be the provincial governor, who was near the explosion but escaped injury.

The U.S. military announced that al-Qaida’s top leader in Mosul, known by his nickname Abu Khalaf, was killed in a raid two days earlier. U.S. officials say Mosul is the last major Iraqi city where al-Qaida has a significant presence.

Thursday’s other bombing took place at a building in Karmah, 20 miles west of Baghdad, where dozens of sheiks had gathered for a meeting attended by U.S. officials, said Col. Fawzi Fraih, civil defense director of Anbar province.

Local police Capt. Amir al-Jumaili said 20 Iraqis were killed and 20 others wounded.