Washington:  "The United States suspects Iranians were directly involved in the January 20 attack on a US compound in Karbala, Iraq, which killed five US soldiers," said sources.

Citing unnamed US government officials, CNN said the Department of Defense is investigating whether the attack, carried out by men wearing uniforms resembling those of US troops, was carried out by Iranians or by fighters taught by Iranians.

"We believe it s possible the executors of the attack were Iranian or Iranian-trained," one of the officials told sources.

"This was beyond what we have seen militias or foreign fighters do," the official said.

The report comes as Washington has stepped up pressure on Tehran to halt its alleged involvement with insurgents and sectarian fighting in Iraq  a charge Iran denies.

President George W. Bush last week authorized US forces to capture or kill Iranian operatives in Iraq.
Bush warned, "If Iran escalates its military action in Iraq to the detriment of our troops and/or innocent Iraqi people, we will respond firmly."