The deadly blast at a US military base near the northern Iraqi city of Mosul that killed 22 people was apparently caused by a suicide bombing, Air Force General Richard Myers, chairman of the Joint Chiefs of Staff, said Wednesday.

"At this point, it looks like it was an improvised explosive device worn by an attacker," Myers said at a Pentagon news conference.

The powerful explosion killed 22 people and wounded 69 in the mess tent of Forward Operating Base Marez near Mosul Tuesday when hundreds of US military soldiers and Iraqi security forces were having lunch.

Of the 22 people killed, 18 were American soldiers or civilian contractors, three Iraqi security force members and one unidentified person, Myers said. Of the 69 people injured, 51 wereUS soldiers or civilian contractors, and five Department of Defense civilians, he said.

But Myers would not say whether the unidentified person killed was the suicide bomber.

US military officials had initially said the blast had been caused by a well-aimed rocket or mortar fired by insurgents outside the base.

The militant Sunni group Ansar al-Sunna issued a statement overthe Internet hours after the explosion taking responsibility for the attack, saying one of its fighters carried out a "martyrdom operation."

Myers said the military would investigate security at the military base, but stressed that it was very difficult to prevent a suicide bomber.

"It's not a viable strategy to ask everybody to separate," Myers said, referring to the large gathering of US military forcesin the tent. "So I think commanders are very much aware of that and try to prevent that."

"We know how difficult this is, to prevent suicide -- people bent on suicide and stopping them," he said.

Defense Secretary Donald H. Rumsfeld echoed Myers' remarks at the same news conference.

"Someone who's attacking can attack at any place at any time using any technique, " Rumsfeld said. "And it is an enormous challenge to provide force protection, something that our forces worry about, work on constantly."

Source: Xinhua