A bomber posing as a taxi driver summoned American troops for help, then blew up his vehicle Saturday, killing himself and four soldiers and opening a new chapter of carnage in the war for Iraq.

Iraq's vice president said such attacks would be "routine military policy" in Iraq -- and, he suggested chillingly, in the United States. Saddam Hussein gave the bomber a posthumous promotion to colonel and two medals -- Al-Rafidin, or The Two Rivers, and the Mother of All Battles, state TV reported.

"We will use any means to kill our enemy in our land and we will follow the enemy into its land," Vice President Taha Yassin Ramadan said at a Baghdad news conference. "This is just the beginning. You'll hear more pleasant news later."

The attack immediately made Americans in the field more wary of civilians, with whom they have frequent contact. Capt. Chris Carter, commander of a company in the same division as the slain soldiers, told his men not to take any chances.

"I'm not going to trust any civilian vehicle," said Carter, of Watkinsville, Ga. "If you see any hostile intent, take it out. Civilians shouldn't be driving around U.S. military vehicles to begin with."

U.S. officials said the bombing occurred at about 10:40 a.m. at a U.S. checkpoint on the highway north of the holy city of Najaf.

A taxi stopped close to the roadblock; the driver waved for help. When soldiers approached the car, it exploded, Capt. Andrew Wallace told Associated Press Television News, killing the driver and four soldiers from the Army's 1st Brigade, 3rd Infantry Division.

Within minutes of the bombing, three other taxis tried to bolt through another checkpoint on the road to Najaf, and Bradley armored vehicles destroyed them, killing an unknown number of Iraqis, a New York Times correspondent with the unit said.

Col. William F. Grimsley, the commander of the 1st Brigade, told the Times it did not appear that those taxis were packed with explosives, but he noted, "it certainly happened near simultaneously."

The names of the Americans were not immediately released. But Ramadan identified the bomber as Ali Jaafar al-Noamani, a noncommissioned army officer and father of several children.

"It's the blessed beginning," the television report said of the suicide attack. "He wanted to teach the enemy a lesson in the manner used by our Palestinian brothers."

It claimed that 11 American soldiers were killed in the attack, two APCs destroyed and two tanks damaged.

"After he kissed a copy of the Quran, he got into his booby-trapped car and went to an area where enemy armored cars and tanks were gathered on the fringes of Najaf and turned his pure body and explosives-laden car into a rocket and blew himself up," the TV report said.

Ramadan said Iraq cannot match American weaponry and has the "legal right to deal with the enemy with any means."

"They have bombs that can kill 500 people, but I am sure that the day will come when a single martyrdom operation will kill 5,000 enemies."

Thousands of Arab volunteers have been pouring into Iraq since the start of the war, he said, adding that Iraq will provide them with what they need to fight the allied forces.

This was the first such attack since the invasion began.

Maj. Gen. Stanley McChrystal of the Joint Chiefs of Staff said suicide attacks would not change the way U.S.-led forces proceed, except that they would take more care in vulnerable locations like checkpoints.

"We're very concerned about it. It looks and feels like terrorism," he said.

Grimsley, commander of the brigade that was hit, said force protection remained the highest priority, "but that doesn't mean we're going to back into little holes and hide."

"The local population that's here and happy that we're here -- they tell us all the time, they've been feeling the same kind of terrorist repression for years and now unfortunately it's hit American soldiers. I think it only tightens the resolve of why we're here."

The soldiers of A Company, 3rd Battalion, 7th Infantry Regiment were stunned by news of the attack -- especially since the men killed were, like them, from the 3rd Infantry Division.

"It's a shame they are doing that because now we're going to have to treat every civilian vehicle like it is hostile," said Staff Sgt. Bryce Ivings of Sarasota, Fla. "If we accidentally kill a civilian because they took a wrong turn and came at us, it will be on their (the Iraqi leadership's) head."

The attack did not come without warning.

Iraqi dissidents and Arab media have claimed that Saddam has opened a training camp for Arab volunteers willing to carry out similar bombings against U.S. forces in Iraq.

Al Qaeda mastermind Usama bin Laden also urged Iraqis in an audio tape on Arabic television last month to employ the tactic, used frequently by Palestinian militants against Israeli soldiers and civilians.

Though the Iraqis said the bomber was an Army officer, Lt. Col. Ahmed Radhi, an exiled Iraqi officer in Cairo, Egypt and former commander of an army brigade, said he did not believe it. The claim, Radhi said, was "a stupid method to raise morale among the army."

If a soldier was involved, Radhi insisted, he either did not know his car carried a bomb or was acting under duress.

In 1970, Saddam sent a group of security officers with a booby-trapped car to kill Kurdish leader Mustafa Barzani, father of Massoud Barzani, current chief of the Kurdistan Democratic Party. The car exploded prematurely, killing the security officers while Mustafa Barzani survived.

The biggest suicide attack against the U.S. military abroad was in Lebanon, when a truck packed with explosives drove into a U.S. Marine base in Beirut and exploded in the early morning of Oct. 23, 1983, as the troops slept. The attack killed 241 American servicemen and leveled the base. A simultaneous suicide attack on a Beirut base for French soldiers killed 58 paratroopers.

The Americans and the French were in Lebanon as part of an ill-fated peacekeeping mission to end Lebanon's civil war. Iranian-backed Shiite Muslim militants were blamed for the attacks.

In 1996, a truck bomb at the Khobar Towers barracks in Saudi Arabia killed 19 U.S. servicemen.