The soldiers, from a unit based in Tikrit, were killed in the town of Samarra, 100km north of Baghdad, the statement said on Thursday. No further details were provided.

More than 60 US troops have died in Iraq this month, including 14 killed by a powerful roadside bomb that hit an armoured Marine transport vehicle near Haditha, west of Baghdad.

Since the start of the war in March 2003, more than 1850 US troops have died in Iraq.

Roadside bombs have been the biggest killers of US forces, being responsible for more than a third of combat deaths, according to the US military.

In recent months, US officials say more powerful bombs are being used against them, similar to "shaped charges", which concentrate the blast in a small area and make it possible to penetrate armour plating.