The U.S. ambassador to Iraq said Saturday that al-Qaida's network in the country has never been closer to defeat, and he praised Prime Minister Nouri al-Maliki for his moves to rein in Shiite and Sunni militant groups.

Ryan Crocker's comments came as Iraqi forces have been conducting crackdowns on al-Qaida militants in the northern city of Mosul and on Shiite militiamen in the southern city of Basra. Thousands of Iraqi forces also moved into the Shiite militia stronghold of Sadr City in Baghdad last week imposing control for the first time in years.

But truces with the powerful Mahdi Army militia that have calmed violence in Basra and paved the way for the Sadr City deployment have been strained in the past two days.

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Supporters of anti-U.S. cleric Muqtada al-Sadr, who heads the Mahdi Army, accused al-Maliki on Saturday of seeking to eliminate their movement and warned that "dark clouds" hang over the truce.

Al-Qaida fighters or other Sunni insurgents struck back in Mosul on Saturday. A roadside bomb in the city's Sumer neighborhood hit an Iraqi army patrol, destroying a vehicle and killing four soldiers, a police officer said on condition of anonymity because he was not authorized to talk to the media.

Near Baqouba — where a U.S. offensive last year targeted al-Qaida in Iraq — gunmen assassinated a member of the local Awakening Council, a U.S.-backed group of Sunni tribesmen who are fighting al-Qaida. The attack occurred in the village of Had, north of Baghdad, police said.