Early on Wednesday, the AC 130 gunship fired 105 and 40 mm rounds at two buildings used to ambush Marines on Tuesday when rocket-propelled grenades disabled two Marine armoured amphibious assault vehicles (AAVs), the marine officer said.
"We're using defensive fire on known enemy positions to protect our Marines," the officer said.
The two buildings were inside Falluja's southern industrial area which is under Marine control.
The Marines denied the strikes marked an end to its halt on offensive operations in Falluja while the US-installed Governing Council engaged in truce talks with members of the city.
On Wednesday, F-15s fired cannons on fighters' positions after the two AAVS were disabled. There was no information immediately available on whether there were any casualties in the ambush.
The F-15 strike was the first since the start of Saturday's truce.
Four US marines have been killed in attacks over the last 48 hours in the al-Anbar province west of Baghdad, the US-led occupation said in a statement on Wednesday.
"Four marines assigned to I Marine Expeditionary Force were killed recently as a result of enemy action in the al-Anbar province," said the statement.
"Two of the marines were killed in action on 13 April; two marines were killed in action on 12 April," it added.