The American command in Baghdad confirmed that two Americans were missing on Friday after insurgents attacked a checkpoint they had set up on a canal crossing near the Euphrates River. One soldier was killed in the attack, which appeared to be an elaborate lure intended to isolate part of the force.

At the time of the attack, the American soldiers were at a traffic control checkpoint on the edge of Karagol. According to the Iraqis, the checkpoint was guarded by about a dozen American soldiers who had arrived in three Humvees.

The checkpoint came under fire from insurgents operating from the fruit groves that line the road. The Americans in two of the Humvees took off in pursuit as the insurgents retreated into the groves, possibly to lure them in, the Iraqis said, leaving one Humvee and only three or four American soldiers at the checkpoint.

The checkpoint then came under attack from another direction by a group of seven or eight guerrillas, wearing kaffiyehs over their faces and black track suits, the Iraqis said. At least one of them carried a heavy machine gun, and two of them carried rocket-propelled grenades.

Minutes after the two Americans were taken away, a team of Americans arrived and began searching door to door in the area, the Iraqis said. By Saturday morning, the search had intensified, with soldiers scouring the area, helicopters surveying the landscape from above and divers going into canals, the American military said in a statement.