A US military spokesman did not give further details on the attack.
RPGs also hit a US tank in the flashpoint town of Fallujah, 50 km west of Baghdad, but it was not clear if there were any casualties.
The ambush appeared to cause little damage, according to eyewitnesses.
Occupation troops say they face almost 13 resistance attacks a day in war-torn Iraq.
In Ba’aquba, about 60 km northeast of the capital, US occupation forces were forced to pull back from guard duties outside the town’s hospital after a series of attacks, including a grenade blast on Saturday that killed three soldiers.
The US military told the Director of the General Hospital that it was no longer safe for his soldiers to be on guard duty and was replacing them with Iraqi police, according to medical sources.
US troops also came under mortar fire overnight at their airbase in Ba’aquba. Reports of mortar salvos have become a daily occurrence in the town.
The US military did not comment on the attacks in Fallujah and Ba’aquba but it did report that two mortar rounds were fired on a base by the northern city of Mosul at 1200 GMT on Tuesday. No casualties were reported.
Meanwhile, US forces continued scouring ousted Iraqi President Saddam Hussein’s hometown of Tikrit for loyalists, after a pre-dawn raid netted a bodyguard of the former leader on Tuesday.
A protester urges
Ordinary Iraqis are growing more frustrated as the US occupying administration fails to restore regular water and electricity supplies.
Hundreds of protesters demonstrated outside the occupation forces’ headquarters in Baghdad on Wednesday for the second time in as many days demanding jobs.
Hundreds of thousands were left unemployed after US occupying administrator for Iraq Paul Bremer sacked government employees.
Meanwhile, in the central holy city of Karbala about a thousand Iraqis protested against what they said is the accessibility to drugs and pornographic films in the area, reported Aljazeera.
Karbala is a mainly Shi’I, conservative city.