Iraq's daily barrage of attacks killed two more American soldiers and an Iraqi employee of a UN-affiliated relief agency, while thousands of followers of a hardline Shiite Muslim cleric staged an anti-American protest in the holy city of Najaf.
Also, the top commander of American and international troops in Iraq said Sunday he is establishing an Iraqi "civil defense force," or armed militia, of about 6,800 men to help American forces combat the violence and sabotage that he and others believe is being spearheaded by remnants of Saddam Hussein's regime.
General John Abizaid, the commander of US Central Command, said he will establish eight battalions of armed Iraqi militiamen, each with about 850 men. They will be trained by conventional US forces -- a job usually handled by American special operations forces -- and are expected to be ready to begin operating within 45 days, he said.
The two US soldiers died when rocket-propelled grenades and small-arms fire struck their convoy early Sunday near Tal Afar, a town west of the northern city of Mosul, said military spokesman Corporal Todd Pruden. Another soldier was injured. All the victims were from the 101st Airborne Division.
The deaths brought to 151 the number of US troops killed in action since the March 20 start of war -- four more than during the 1991 Gulf War. Also Sunday, a US soldier was killed and two others injured when their vehicle crashed and flipped over near Baghdad International Airport, according to a statement from US Central Command in Tampa, Florida.
The area of the convoy attack near Tal Afar, 385km northwest of Baghdad, had been relatively peaceful in recent weeks, and the ambush was a worrying development for American forces trying to bring stability to Iraq.
Most recent violence has occurred in an area north and west of Baghdad called the Sunni triangle, where support for Saddam remains. Tal Afar lies outside that region.
On Sunday, the top US official in Iraq said he believes Saddam is still alive and in the country, though not orchestrating attacks on American troops.
Paul Bremer, speaking to NBC's Meet the Press, said there was no evidence of central control in the assaults, calling them "highly professional but very small, sort of squad-level attacks, five or six people at a time attacking us."
Still, he said, getting Saddam would help the situation.
"The sooner we can either kill him or capture him, the better, because the fact that his fate is unknown certainly gives his supporters the chance to go around and try to rally support for him," said Bremer.
In another troubling sign, a two-car convoy carrying members of the International Organization for Migration were ambushed near the southern city of Hilla when a pickup truck pulled up alongside one car and opened fire.
The car collided with a bus. Personnel in a World Health Organization convoy traveling behind the IOM vehicles treated three injured and took the Iraqi driver to a hospital, where he died, said Omer Mekki, the WHO deputy director in Iraq.
Both convoys were clearly marked as UN vehicles.
"We're a bit shaken. Everybody is a bit shocked," said Mekki. "But when we were recruited and we came to Iraq, we knew there were risks. An incident like this is not unexpected."
Ahmed Fawzi, spokesman for the special representative of UN Secretary-General Kofi Annan, denounced the attack. "The United Nations is in Iraq to help the Iraqi people. We are not taking sides," he said in Baghdad.