A barrage of mortar fire slammed into Baghdad's heavily fortified Green Zone at dawn on Sunday, followed by a fresh attack four hours later, officials and witnesses said.
There were no immediate reports of casualties, US embassy officials said.
Black smoke was seen rising from the Green Zone, the seat of the Iraqi government and the US embassy also known as the International Zone, immediately after the 6:30 am (0330 GMT) and 10:30 am (0730 GMT) attacks.
An employee in the Green Zone, Mohammed al-Dulaimi, who witnessed the second attack, said eight mortar rounds fell near the US embassy complex and two a little distance away in a residential area.
"They caused slight damage and one sparked a fire," Dulaimi told AFP.
A US embassy spokesman confirmed both attacks and said there were no immediate reports of casualties.
"I heard the blasts. We are checking damage. We have no reports of casualties," the spokesman said.
He was unable to say whether the mortar rounds landed near the embassy. "All I can say is that they fell in the International Zone."
US embassy spokeswoman Mirembe Nantongo told AFP after the first attack that an initial assessment did not indicate any "death or major casualties."
Insurgents and militiamen regularly fire mortars or rockets at the Green Zone, one of the most secure areas in Baghdad.
The US military claims that most mortar rounds or rockets that hit the area are manufactured in Iran and fired by "rogue" elements of radical Shiite cleric Moqtada al-Sadr's Mahdi Army militia.
