BAGHDAD - The U.S. ambassador to Iraq said yesterday that al-Qaeda'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-Qaeda 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 last two days.

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

Al-Qaeda fighters or other Sunni insurgents struck back in Mosul yesterday. 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.

Near Baqubah - where a U.S. offensive last year targeted al-Qaeda in Iraq - gunmen assassinated a member of the local Awakening Council, a U.S.-backed group of Sunni tribesmen who are fighting al-Qaeda.

Crocker spoke as he visited reconstruction projects in the southern city of Najaf.

"There is important progress for the Iraqi forces in confronting the Sunni and Shiite militias," he said, speaking Arabic to reporters. "The government, the prime minister are showing a clear determination to take on extremist armed elements that challenge the government's authority . . . no matter who these elements are."

"You are not going to hear me say that al-Qaeda is defeated, but they've never been closer to defeat than they are now," Crocker said.

The U.S. military says attacks have dropped dramatically - down to an average of 41 a day across the country, the lowest rate since 2004 - amid the crackdowns and truces.