The US military says three American Marines and two interpreters have been killed in an attack west of Baghdad in Anbar province. Iraqi police say the attack was carried out by a suicide bomber against a meeting of pro-government Sunni sheiks in the former insurgent stronghold and at least 20 Iraqis were killed as well. The military statement gives the death toll but does not provide more details about the attack. Anbar province has seen a steep decline in violence in the past year thanks to the Sunni revolt against al-Qaida in Iraq. But Thursday's attack underscores the fragility of the security gains.