Iraq's Fallujah, encircled by US and Iraqi governmental troops ready for a major assault, was pounded in what appeared to be the latest round bombardments late Saturday.
The strikes started before midnight, local residents told Xinhua, adding that US war planes dropped bombs in three neighborhoods inside the city and artillery fire hit an area in the east.
Some witnesses said they believed the insurgents launched an anti-air weapon which probably struck a US helicopter, but the report could not be confirmed by the US military.
There was no report of casualties in the fresh fighting and the hospital could not be reached during the time of ongoing bombings.
A series of air and ground fire strikes late Friday and early Saturday left at least three people dead and seven others injured, including some women and children.
A US statement said the coordinated precision strikes destroyed three barricaded fighting positions, an anti-aircraft weapon and a weapons cache in the Fallujah-Ramadi area.
Meanwhile, US and Iraqi troops trained to face the Fallujah offensive were taking positions around the outskirts, while warning the citizens to desert the city. Over half of the about 300,000 residents have so far fled.
Also on Saturday, a US spokesman said around 20 US marines were injured in action while conducting an increased security operation in Ramadi, another flashpoint city near Fallujah.
He gave no further details about the incident, one of the fiercest attack faced by Americans in the area.
The two cities, both west of Baghdad, were on the top list of restive places to be retaken from rebel's hands to pave the way for the nation-wide elections due in January.