BAGHDAD: The US military says two American soldiers have been killed by a roadside bomb outside the main US base in Baghdad.

Two military officials said Thursday's bomb at a checkpoint outside Victory Base Camp used armor-piercing explosives known as EFPs.

The powerful bombs are the trademark of an Iranian-backed Shia militia.

The two soldiers were not identified pending notification of next of kin. No other details were immediately available, and the officials spoke on condition of anonymity because the details were not publicly released.

Victory Base is the headquarters of the US military in Iraq.

Thursday's deaths bring to 4,471 the number of American troops who have died in Iraq since the 2003 invasion.