An al-Qaida front group threatened to assassinate Sunni leaders who support American troops in Iraq as a Shi'ite bloc loyal to radical cleric Muqtada al-Sadr defected from the Iraqi government's parliament base.
The two developments Saturday cast doubt over prospects for political and military progress in Iraq as the US Senate gears up for a debate next week on Democratic demands for deeper and faster troop cuts than US President George W. Bush plans.
The threat against Sunni leaders came from the Islamic State of Iraq, which claimed responsibility for the assassination Thursday of Abdul-Sattar Abu Risha, the mastermind of the Sunni Arab revolt against al-Qaida in Anbar province. Bush met Abu Risha at a US base in Anbar this month and praised his courage.
In a Web posting, the Islamic State said it had formed "special security committees" to track down and "assassinate the tribal figures, the traitors, who stained the reputations of the real tribes by submitting to the soldiers of the Crusade" and the Shiite-led government of Prime Minister Nouri al-Maliki.