The car bomb was set off just after sundown outside a Shia mosque in the Musayyib city, the local security source said.

On July 16, more than 90 people were killed when a suicide bomber set off a massive fireball in the centre of Musayyib when he blew himself up next to a liquefied tanker outside a Shia mosque.

Earlier four US servicemen have been killed in and around the restive western Iraqi town of Ramadi, including two US marines who died in the crash of their attack helicopter, the military said yesterday.

There was no immediate word on the cause of Wednesday morning's crash, but in a separate statement the military said an F-18 fighter jet bombed a suspected insurgent command centre 500 metres (yards) from the site of the crash a few hours after the helicopter went down.

The crash occurred "while the two-man crew was flying in support of security and stabilisation operations," the military said.

Another marine and a sailor serving with the marine expeditionary force were also killed when their vehicle was hit by a roadside bomb in Ramadi on Tuesday, the military added.

The deaths brought to at least 2,026 the number of US military personnel who have died in Iraq since the March 2003 invasion, according to an AFP tally based on Pentagon figures.

The Iraqi defence ministry yesterday called on all former officers of Saddam Hussein's disbanded armed forces up to the rank of major to join the new army.