US warplanes and helicopter gunships firing heavy machine-guns, rockets and cannons have attacked Iraqi positions in Fallujah as a truce in the town was strained by increasingly intensive gun battles today.
April has became the deadliest month for American forces since they set foot in Iraq.
Elsewhere, a 2,500-strong American force are massed on the outskirts of the Shiite holy Najaf for a showdown with a radical cleric, raising fears of an attack on the city that would outrage the nation's relatively pro-US Shiite majority.
Russia has announced that it will evacuate its citizens from Iraq following a spate of kidnappings of more than 40 foreigners that erupted with the violence this month.
US troops were holding back on both fronts to allow Iraqis to try to negotiate a resolution, but President George Bush said last night he was prepared to send more troops and instructed his commanders to be ready to use "decisive force."
"Our work may become more difficult before it is finished," Mr Bush said. "No one can predict all the hazards that lie ahead or the cost that they will bring. Yet, in this conflict, there is no safe alternative to resolute action."
With the announcement of the deaths of four more marines, April became the deadliest month for the US military in Iraq - deadlier even than the invasion launched in March 2003. At least 87 troops have been reported killed in action in less than two weeks. Previously, November had seen the most deaths, 82.
Some 880 Iraqis have been killed this month. Among those are more than 600 - mostly civilians - killed in Fallujah, according to the city hospital's director.
A US Cobra attack helicopter fired rockets and heavy machine-guns before dawn today at gunmen gathered on the northern edge of the city of Fallujah.
Rocket-propelled grenades arched up from the ground toward the helicopter and a second gunship providing support, but none apparently hit the gunships.
Earlier, A-130 gunships pounded a row of buildings from which marines say ambushes have repeatedly been launched in a residential area of the city.