Pentagon officials complained bitterly Monday about what they called "deadly deceptions" by Iraqi troops pretending to surrender to U.S. forces and then firing on the Americans.

"They are sending forces out carrying white surrender flags or dressing them as liberated civilians to draw coalition forces into ambushes," said Victoria Clarke, spokeswoman for Defense Secretary Donald H. Rumsfeld. "Both of these actions are among the most serious violations of the laws of war," she said.

Maj. Gen. Stanley McChrystal, vice director of operations on the Pentagon's Joint Staff, said U.S. forces would continue to accept Iraqi surrenders.

In two episodes Sunday near An Nasiriyah, Iraqi forces deceived Americans into believing they were surrendering or otherwise welcoming them, U.S. officials said.

The officials said one unit indicated it was giving up but as Marines approached the Iraqis opened fire, killing nine Americans. U.S. military sources said about 40 were wounded.

"Some liken these acts to terrorism," Clarke said. "Such acts involve the enemy willfully violating the laws of war, while simultaneously taking advantage of the coalition forces' compliance with that law."

McChrystal said, meanwhile, that allied forces began to shift attention Monday to the Iraqi Republican Guard troops protecting Baghdad -- in particular the Medina armored division south of the capital.

Army Apache helicopters attacked with Hellfire tank-killing missiles and allied warplanes carried out their heaviest bombing against the Republican Guard so far.

At least one Apache was downed and Iraq said it had captured two pilots.

McChrystal said U.S. ground troops had not yet engaged Iraqi Republican Guard units in direct combat, other than the attacks by Apaches. He said the helicopter attacks were according to military doctrine -- combining deep strikes with psychological operations and, soon, artillery fire, to weaken the Medina division before the U.S. 3rd Infantry Division hits it full force.

McChrystal expressed regret about a U.S. bomb that hit a passenger bus near the Syrian border carrying civilians. Five Syrians were killed and 10 wounded in the incident, according to Syria's official news agency.

McChrystal said the weapon fired by an Air Force A-10 attack plane was aimed at a bridge 100 miles from the Syrian border. "A bus came into the pilot's view too late to recall the bomb aimed at the bridge," he said. "Unintended casualties like this are regrettable."

Asked about the relatively slow pace of Iraqi surrendering, McChrystal suggested that members of the Fedayeen, Saddam Hussein's most trusted militia, had infiltrated regular Iraqi army units, telling them to "fight or be shot in the back."

He suggested that all phases of the U.S.-British military operation were on track.

"We are on the timeline, if not slightly ahead of the schedule that Gen. (Tommy) Franks has set," he said. Franks is the commander of all the allied forces in the war.

American forces chased down leads from captured Iraqis and from documents on possible chemical and biological weapons sites, but as of Monday could not confirm the presence of any weapons of mass destruction.

A suspicious plant captured by American troops was being evaluated, other officials said.

Earlier, at Central Command headquarters in Qatar, Franks said, "It would not surprise me if there were chemicals in the plant and it would not surprise me if there weren't."

Iraq claims it destroyed all of its chemical and biological weapons and ended its nuclear weapons program shortly after the 1991 Persian Gulf War. U.N. weapons inspectors say those claims are highly suspect -- and the United States says they are lies.