Washington's No. 2 diplomat said political progress must quickly follow the security gains from the influx of American troops in Iraq, warning Sunday that the country risks "falling back to the more violent patterns of the past."

By KIM GAMEL BAGHDAD - A bomb in a parked car struck worshippers heading to a Shiite mosque Sunday in Baghdad, killing at least nine people as Iraqis celebrated a Muslim holiday, while the death toll rose to 18 in a coordinated suicide truck bombing and ambush north of the capital.

A car bomb exploded Saturday near Baghdad's most important Shiite shrine, killing seven people and wounding dozens as authorities imposed new security restrictions to prevent attacks on Shiite pilgrims ahead of major religious ceremonies south of the capital.

Sixty suspected al-Qaida in Iraq fighters hit national police facilities in a coordinated attack in Samarra, sparking two hours of fighting that saw three people killed and more than a dozen insurgents captured, police said Friday.

U.S. troops killed the al-Qaida in Iraq mastermind of the bombing that destroyed the golden dome of a famed sacred Shiite shrine last year and set in motion an unrelenting cycle of sectarian bloodletting, the military said Sunday.