Four U.S. contractors were killed last month when their convoy took a wrong turn, drove into a town north of Baghdad and was attacked by an angry mob, a senior U.S. military official said Saturday.

The incident, which occurred Sept. 20 in the town of Duluiyah, about 45 miles north of Baghdad, was first reported Saturday by Britain's Daily Telegraph. The senior U.S. military commander confirmed the account to The Washington Post. There was no explanation for why the military did not report the deaths earlier.

The commander said the four men -- identified by the Telegraph as employees of the Halliburton Co. subsidiary Kellogg Brown & Root -- realized their convoy had taken a wrong turn and were desperately trying to escape from the town when their vehicle was attacked by insurgents.

The Telegraph said "dozens of Sunni Arab insurgents wielding rocket launchers and automatic rifles" pursued their truck and shot at it.

Two contractors who were not killed in the initial firing were dragged from their vehicle, and one was shot in the back of the head, the newspaper said. The crowd "doused the other with petrol and set him alight. Barefoot children, yelping in delight, piled straw on to the screaming man's body to stoke the flames," according to the report.

The crowd then "dragged their corpses through the street, chanting anti-U.S. slogans," the newspaper reported.

Details of the account could not be independently verified. The incident is reportedly under investigation.

"Soldiers responded to assist the convoy, administered first aid to two wounded contractors and evacuated the remains of four wounded contractors killed in the attack," a military spokesman told the Reuters news service in a statement Saturday.

American soldiers who were escorting the convoy were unable to respond quickly enough to save the men, according to a U.S. military officer who interviewed soldiers involved in the incident and who spoke to the Telegraph. "The hatches of the Humvees were closed," the officer, Capt. Andrew Staples, told the newspaper.

The incident recalled a similar one in March 2004, when a mob in the insurgent stronghold of Fallujah killed four U.S. security contractors, mutilated their bodies and hanged them from a bridge.

The September killings bring to about 320 the number of non-Iraqi civilian contractors killed in Iraq since the start of the war in April 2003, according to statistics complied by the Brookings Institution.

Meanwhile, three U.S. Marines and one Army soldier were killed in attacks earlier in the week, the military said in statements Saturday, pushing the total number of U.S. military deaths close to 2,000 since the start of the Iraq war.

The three Marines were killed Friday -- two when their vehicle was hit by a roadside bomb near Amariyah, about 25 miles west of Baghdad, and the other when he was "hit by an explosion" during a fight with insurgents near Haqlaniyah, about 80 miles from the Syrian border, the military said.

The military reported that the Army soldier died on Thursday "of a non-hostile gunshot wound," a term that usually means an accidental death or suicide. According to a recent report by the Center for Strategic and International Studies in Washington, 299 U.S. soldiers have died of accidental causes in Iraq and 48 have committed suicide.

In fighting Saturday, U.S.-led forces reported killing 20 "terrorists suspected of sheltering al Qaeda in Iraq foreign fighters" in a series of raids on safe houses near Husaybah, a border town with Syria along the Euphrates River, a military statement said.

Another statement said that U.S.-led forces found a huge weapons cache in Rawah, a town about 45 miles from the border along the Euphrates, in search operations last week. Military officials say that the Euphrates River is a major transit route for foreign fighters and supplies that are fueling the insurgency here.

Electoral officials in Baghdad said Saturday that an audit of votes from the Oct. 15 constitutional referendum had so far uncovered no evidence of fraud. The audit was initiated because of the unusually high number of votes in favor of the constitution in some areas of the country. Officials said full preliminary results were expected to be released within a few days.