Halliburton says the workers were Steven Hulet of Michigan, Jack Montague of Illinois, and Jeffrey Parker of Louisiana.
They were among seven workers for a Halliburton subsidiary missing since the April ninth attack.
That followed an attack March 31 in Fallujah in which private American security workers were killed, and their bodies mutilated by a crowd.
In Mosul a roadside bomb exploded as a U.S. military convoy passed by, killing a U.S. soldier and wounding four others, the military said. Three Iraqi civilians were also wounded, Lt. Col. Joseph Piek said. The death brought to 100 the number of U.S. troops killed in action in April month.
Meanwhile, a barrage of 18 mortars hit a Baghdad jail, killing 22 prisoners, the U.S. military said. Brig. Gen. Mark Kimmitt said the mortar strike hit the Baghdad Confinement Facility run by the U.S.-led coalition. Ninety-two prisoners were wounded in the attack, 25 of them seriously, said Col. Jill Morgenthaler, a U.S. military spokeswoman.
In other developments:
Security forces and civilians who fled days of street fighting in Fallujah began to return Tuesday in a critical test of an agreement between U. S. officials and local leaders to end the American siege of the rebellious city.
A U.S. military-run radio station urged residents to hand over heavy weapons — including machine guns, grenade launchers and missiles — to Iraqi security forces or at the mayor's office.
But it was not yet known whether guerrillas would abide by the call to surrender their arsenals. U.S. commanders have warned Marines might launch an all-out assault to take the city if the insurgents don't disarm.
By midday Tuesday, up to 200 members of the Iraqi security forces had returned to their jobs.
Dozens more police — wearing blue uniforms and flak jackets and carrying weapons — lined up at a Marine checkpoint to enter the city in the afternoon. Iraqi families lined up there as well to go home.
About a third of the city's 200,000 people fled during the two-week siege that killed at least 600 Iraqis, according to hospital officials.
As part of a deal announced Monday, the military agreed to let 50 families a day back into the city, but people kept showing up after that limit was reached. About 150 people had to be turned away, said Capt. Ed Sullivan.
Whether the peace holds depends on whether the Fallujah civic leaders who reached the deal with the Americans can persuade the insurgents to disarm — or whether the Iraqi police forces are effective in uncovering weapons.
For the city's guerrillas, any hand-over of their heavy weapons would mean weakening, if not ending, their months-long resistance against the U.S.-led occupation. The insurgents have gone to great lengths to build up their arsenal and hide it — Marines in the past two weeks have found impressive caches in secret rooms hidden by mirrors and buried in yards.
Meanwhile, U.S. and coalition military leaders were trying to work out how to fill the gap left by the abrupt decision by Spain and Honduras to withdraw their troops from the country.
Kimmitt sought to allay fears about the implications of the Spanish pullout, saying there would be no "security vacuum in that area at any time."
But it remains unclear who will take the place of departing troops. The 9,500 international peacekeepers under Polish command are charged with the south-central sector, where followers of radical Shiite cleric Muqtada al-Sadr are waging a bloody rebellion.
Spain's decision was a setback for the Bush administration, which has been eager to portray the effort in Iraq as an international cause even though it is dominated by 130,000 American troops.
Aside from the U.S. and multinational forces, some 12,000 British troops and 2,700 Italians operate in the far south.
President Bush scolded Spanish Prime Minister Jose Luis Rodriguez Zapatero for the abrupt withdrawal, telling him in a telephone conversation Monday to avoid actions that give "false comfort to terrorists or enemies of freedom in Iraq."
Albania immediately said it was ready to increase its small presence. Ukraine, Australia, Portugal, Slovakia, San Salvador and the Dominican Republic said their commitments to the force would not waver. And Thailand's prime minister said he is not rushing to pull troops out because the security situation there has not deteriorated that badly.