Guerrillas fired a rocket this evening at the Baghdad compound where the US-led administration in Iraq is based, the US Army said, but caused no casualties.
A military spokesman said the rocket landed in an open area in the "green zone", a sprawling palace complex formerly used by Saddam Hussein which now houses the headquarters of the US-led civil and military administration.
"It landed in an open parking lot in the green zone. There were no casualties and no damage to property or equipment," the spokesman said.
A loud explosion echoed across central Baghdad when the rocket landed, followed by warning sirens.
"Take cover, take cover," said a warning message played over green zone loudspeakers after the blast.
The compound on the west bank of the Tigris river has come under rocket and mortar attack several times in recent months.
Just over a week ago a suicide bomber detonated half a tonne of explosives outside the US seat of power in Iraq, killing at least 25 people in the deadliest attack since the capture of Saddam.
Two United Nations security experts are in Iraq assessing whether the country is safe enough for UN staff to return to assist in transferring sovereignty back to Iraqis.