Four occupying American soldiers were killed by a roadside bomb explosion in Diyala province northeast of Baghdad, the desperate military said on Saturday.

The blast took place near the soldiers' vehicle on Friday, a military statement said without providing further details.

The names of the soldiers are being withheld pending notification of next of kin, it added.

The latest death brings the number of American soldiers who have been killed in Iraq to about 3,780 since the outbreak of the Iraq war in 2003, based on Pentagon figures, but unofficial sources across Iraq put the figure at much higher.

Some political observers believe that the presence of foreign occupying forces remains behind insecurity in the oil-rich country.