Meanwhile, the Philippines government rejected an insurgent group's ultimatum to pull its small peacekeeping force out of Iraq. The group has threatened to kill a Filipino man it is holding hostage.
A roadside bomb attack on a U.S. patrol in the city of Samarra, a hotbed of violence 60 miles north of Baghdad, killed two soldiers on patrol Sunday afternoon and wounded three others, the military said.
An earlier attack on a U.S. convoy in Beiji, 90 miles south of the northern city of Mosul, began Sunday morning when a roadside bomb exploded next to the patrol, the military said.
An enemy vehicle then raced toward the convoy, firing at the soldiers, who shot back and killed the driver, the military said.
A soldier and a civilian traveling behind the patrol were killed. A second soldier was injured and evacuated. Thick black smoke poured over the area from an oil tanker set alight in the attack.
The deaths came a day after four U.S. Marines were killed in a vehicle accident near Camp Fallujah in western Iraq. More than 875 service members have died since the beginning of military operations in Iraq.
In other developments:
Militants from a group calling itself "The Iraqi Islamic Army-Khaled bin Al-Waleed Corps" gave the Philippines a Sunday night deadline to agree to withdraw its 51-member peacekeeping force by July 20 — a month ahead of schedule. The group threatened to kill truck driver Angelo dela Cruz if the Philippines did not comply.
After an emergency Cabinet meeting Sunday, the Philippines government refused.
"In line with our commitment to the free people of Iraq, we reiterate our plan to return our humanitarian contingent as scheduled on Aug. 20, 2004," Foreign Secretary Delia Albert told reporters.
Dela Cruz's wife and brother were heading to Baghdad, Albert said, and the government remained hopeful he would be released.
Philippine negotiators were working through mediators Sunday to try to free dela Cruz, a diplomat in Baghdad with knowledge of the situation said.
A deadline for two other hostages, a pair of Bulgarian truck drivers held by a separate group demanding the release of all Iraqi detainees, expired Saturday morning. Bulgarian Foreign Minister Solomon Pasi said Sunday he had unconfirmed information they were alive.
At a news conference in Bulgaria, Pasi appealed to the hostage takers, saying Islam calls for "mercy for the poor, the hungry and the sick." He said one hostage, Georgi Lazov, had diabetes, while the other, Ivaylo Kepov, had suffered a stroke.
The group holding the Bulgarians, the Tawhid and Jihad movement linked to Jordanian terror suspect Abu Musab al-Zarqawi, also claimed responsibility Sunday for a Thursday attack on a military headquarters in the city of Samarra that killed five U.S. soldiers and an Iraqi National Guardsman.
To prevent the infiltration of foreign fighters, Syria and Iraq agreed to set up a special force to patrol their 360-mile shared border, Iraqi Deputy Prime Minister Barham Saleh said Sunday in Damascus, Syria, after meeting with Syrian President Bashar Assad.
In other developments, Iraq's national security adviser, Mouwaffaq al-Rubaie, said Sunday the country would never again threaten its neighbors and would honor the Nuclear Nonproliferation Treaty as well as international agreements banning the use of chemical and biological weapons.
"Iraq officially declares it will be a country free of any weapons of mass destruction," al-Rubaie told reporters during a news conference. "Iraq will never again resort to threatening its neighbors, as Saddam did."
Saddam's alleged possession of such weapons was one of President Bush's declared reasons for invading Iraq last year. The hunt for weapons of mass destruction has proved largely unsuccessful.
Demonstrators, some supporting Saddam's ousted regime, others opposed to it, took to the streets of Iraq on Sunday.
In Baqouba north of Baghdad, about 100 people marched through the shopping district, chanting pro-Saddam slogans, waving rifles and carrying posters of the former leader. Meanwhile, demonstrators in Baghdad held a mock trial and execution of Saddam, hoisting an effigy from a hangman's noose setting it on fire.
Also Sunday, Islamic militants in Baghdad opened fire on a downtown shop selling alcohol, destroying the merchandise and kidnapping an employee, witnesses said.
"They came in two cars and shouted "God is Great," as they opened fire," said Rafid Fadil, a witness.