The explosion that devastated a US military mess hall in northern Iraq on Tuesday, killing 22 people, including 19 soldiers, was apparently caused by a suicide bomber who infiltrated the American base, according to chairman of the US joint chiefs of staff, General Richard Myers.

"At this point, it looks like it was an improvised explosive device worn by an attacker," Gen Myers said in Washington, DC on Wednesday evening.

He said more would be known shortly when investigators conclude their inquiry into the cause of the explosion.

The attack, which took place as the soldiers were about to eat lunch, was initially thought to have been carried out with a rocket or mortars.

But officials at the base said yesterday there was only one explosion and that a bomb inside the facility had not been ruled out, The Washington Post reported.

An Islamic group that claimed responsibility for the attack, the Army of Ansar al-Sunna, said in a statement posted on the Internet that it had carried out a "martyrdom operation", a term usually used to describe a suicide bombing.