Four US soldiers were killed in two separate incidents in central Baghdad on Tuesday, after the death of four others on Monday in a bombing incident south of the capital.

The US military said in a statement on Tuesday three soldiers had died when a bomb exploded as their convoy drove by, and a fourth was killed 30 minutes later in a separate incident when gunmen shot him from a passing car.

Four US soldiers were also killed in a bomb explosion on Monday near Haswa, about 50km south of Baghdad, the statement added.

The latest fatalities raising the total number of US service personnel who have died in Iraq since the March 2003 invasion to over 1631.

In a separate development, Syria on Tuesday announced that it had ceased cooperation with the CIA and the US army in the wake of what it described as "unfair" allegations by Washington against Damascus.

Syria's ambassador to Washington Emad Mustafa said: "It seems that the US administration has decided to step up pressure on Syria even though the country has completed the withdrawal of its troops from Lebanon and adopted strict measures to prevent the infiltration of armed men from its territory into Iraq."