2 U.S. soldiers killed by a roadside bomb in Iraq

A roadside bomb killed two U.S. soldiers Thursday outside the main American military base in Baghdad, the Associated Press reports.

Thursday's bomb, which was detonated near a checkpoint outside Victory Base Camp, was a powerful armor-piercing explosive known as an EFP, according to two military officials with knowledge of the attack, the source reports.

EFPs typically are designed and outfitted in Iran, and are a trademark of the Shiite militia headed by anti-U.S. cleric Muqtada al-Sadr.

U.S. officials said it appeared to be another attack by Shiite militias hoping to drive U.S. troops out of Iraq.

A spokesman for the U.S. military in Iraq did not have an immediate comment about the attack.

The most recent attack brings the number of U.S. troops who have died in Iraq to 4,471 since the 2003 invasion, according to an Associated Press count.