"Two US marines were killed in action and four US marines were wounded in action today," a US military spokesman said in a short statement released late on Thursday.

The incident took place in al-Anbar province, which houses the rebel hotspots of Fallujah and Ramadi, west of Baghdad, but the spokesman provided no further details about how the casualties happened.

US troops have massed around the two cities in recent weeks, which they believe are the nerve centres of rebel activity in Iraq, amid mounting expectations of a double-pronged assault.

The US-backed government of Prime Minister Iyad Allawi has pledged to crush pockets of resistance ahead of national elections promised by January.

To this end, US war planes launched five air strikes against suspected insurgent positions in Fallujah in the last 24 hours.

"Iraqi security forces and the 1st Marine Expeditionary Force continue to degrade and disrupt anti-Iraqi (insurgent) forces in the Fallujah-Ramadi area," a military statement said.

Starting at 4:40 pm (1340 GMT) Thursday and ending at 1:10 am Friday, planes supporting US marines on the ground destroyed suspected rebel fortifications and a weapons cache in the southeast and northern Fallujah, it said.

Since Monday, Multi-National Forces-West have also captured and destroyed large numbers of mortars, rockets and other explosives.

In Ramadi, the capital city of al-Anbar province, a marine operation discovered and disarmed a youth centre that had been rigged with explosives and found more that two tons of explosives hidden in a mosque.

"The discoveries were made during a sweep of the city looking for improvised explosive devices," the military said in a separate statement.

Fifty suspected insurgents were also netted in the sweep, it added.

The stepped-up strikes against Fallujah and operations in Ramadi came after the re-election of US President George W. Bush, who pledged to ensure that elections due to be held in Iraq in January are a success.

Thousands of residents have fled Fallujah since the US military began a campaign of air strikes during the summer in the hunt for Islamic militant Abu Musab al-Zarqawi and his followers who are believed to use the city as an operating base.

Zarqawi, a Jordanian national who is Iraq's most wanted man, is blamed for some of the worst bombings and kidnappings in the country since last year's US-led invasion.

US ground troops have encircled Fallujah since mid-October, and Allawi issued an ultimatum to the city on Sunday to surrender insurgents holed up inside or face an all-out military assault.

The latest deaths brought to 1,120 the number of US military personnel killed in Iraq since the US-led invasion in March 2003, according to a Pentagon tally.

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