In Baghdad, two Iraqis were killed when their car approached a U.S. military checkpoint.
The killings of the Americans were further signs that an Iraqi insurgency is not losing strength as Washington hoped after the deaths Tuesday of Saddam Hussein's sons, Odai and Qusai.
Arab satellite broadcaster al-Arabiya aired a tape of what it said were a group of Saddam Fedayeen vowing revenge for the deaths of Odai and Qusai Hussein.
"We want to say to the occupation forces, they said last night that killing Odai and Qusai will diminish (resistance) attacks but we want to say to them that their death will increase attacks against them," one of three masked men in the tape read from a statement.
In other developments:
V Corps spokeswoman Spc. Nicole Thompson said the soldiers who were killed, members of the 101st Airborne Division, were traveling in a convoy toward Qayyarah, 185 miles north of the capital, Baghdad, when they were attacked at about 2:30 a.m. No soldiers were reported wounded and it was not known whether any assailants were killed or wounded.
It was the second attack in two days that killed members of the division, which led the fiery assault in the northern Iraqi city of Mosul that killed Odai and Qusai Hussein.
On Wednesday, two American soldiers were killed in separate attacks on their convoys, including one near Mosul.
The latest deaths brought to 158 the number of U.S. servicemen killed in action since the war began March 20, surpassing by 11 the death toll in the 1991 Gulf War.
Odai and Qusai were Nos. 2 and 3 on the U.S. list of 55 most-wanted from the toppled Saddam regime. Guerrilla holdouts loyal to the regime have attacked U.S. forces at a rate of about 12 times a day in an effort to wear down the Americans and drive them from the country.
It was hoped that the deaths of Saddam's sons would have a major impact on the Iraqi resistance, which has been mounting about a dozen attacks a day against U.S. occupation troops.
The guerrillas are thought to be former military officers and Baath Party leaders loyal to Saddam and his family, especially the sons, who played primary roles in the military and feared security services.
However, some U.S. soldiers admit they're worried about revenge attacks after the killings of Saddam's sons. One Army sergeant says, "if one of my sons was dead, I'd want somebody to pay for it."
In a CBS News interview, Abdul Bari al Atwan, editor of the Arabic newspaper Al Quds, suggested the killing of Saddam's sons might backfire on the U.S. "I disagree with the opinions that this will actually make Iraq safer and put an end to the resistance," said al Atwan. "I believe it will fuel the resistance."
In an effort to convince skeptical Iraqis that the feared brothers were dead, the U.S. military released photographs of their bodies Thursday morning. Many Iraqis, especially Saddam supporters, believed the story of the brothers' killing was concocted by the American military to demoralize opponents of their occupation of the country.
In Sadr City, a poor suburb of Baghdad formerly called Saddam City, some residents said they needed proof that the brothers were dead.
"We heard about Odai and Qusai being killed and, frankly, we are happy," Fadil Abbas told Associated Press Television News. "The question is, what's the proof of them being killed? We heard about it, but we haven't seen any proof so far."
In Baghdad, some members of Iraq's Governing Council were shown the brothers' bodies, which are being kept at Baghdad International Airport, said a spokesman for the Coalition Provisional Authority.
Lt. Gen. Ricardo Sanchez, commander of coalition troops in Iraq, said the brothers — along with two other Iraqis believed to be a bodyguard and Qusai's teenage son, Mustafa — barricaded themselves on the second floor of a three-story home in Mosul. He said they were killed after anti-tank rockets were fired from Humvees during a four-hour siege.