KABUL, Afghanistan: American troops raked a large passenger bus with gunfire near Kandahar city on Monday morning, killing at least five civilians and wounding 18, Afghan authorities and survivors said.

The attack infuriated Kandahar leaders and could harm public opinion on the eve of the most important offensive of the war, which is intended to take control of the Kandahar region from the Taliban this summer.

Hundreds of demonstrators poured into the area around a bus station on the western outskirts of Kandaharcity, shouting anti-NATO chants and blocking the road for one hour, according to people in the area.

The bus driver and one of the passengers said that an American convoy 60 to 70 yards ahead of the bus opened fire as the bus began to pull to the side of the road to allow another military convoy traveling behind to pass.

The two convoys and the bus were on the main highway in Sanzari, about 15 miles, or 24 kilometers, west of Kandaharcity. All of the windows on one side of the bus were shot out.

Troops opened fire on the bus just after daybreak as it was taking scores of passengers to Nimroz province, said Zalmy Ayoubi, a spokesman for the Kandaharprovincial governor.

Some of the wounded were in critical condition, and the death toll could rise, local officials said.

Mr. Ayoubi said five civilians had been killed, including one woman.

The Interior Ministry in Kabul issued a statement saying four civilians had been killed and 18 wounded, blaming “NATO forces” traveling in front of the bus for the shooting.

An American military spokesperson put the casualty toll at five dead — all men — and said four others had been wounded, but added that other details would be made public later.

Mr. Ayoubi, the provincial spokesman, said, “We strongly condemn this action carried out by NATO forces, and we want a thorough investigation of the incident, to find out why they targeted the civilian bus.”

If the Afghan government’s casualty toll is correct, it would imply that troops fired scores or even hundreds of rounds. It was not immediately clear why such a large fusillade would have been directed at a passenger bus.

“An American convoy was ahead of us and another convoy was following us, and we were going to pull off of the road, and suddenly the Americans opened fire,” said one passenger, Nida Mohammed, who suffered a shoulder injury.

“We were not close to them, maybe 60 yards away from their convoy,” Mr. Mohammed said.

A helicopter evacuated some wounded, he said.

“This bus wasn’t like a suicide bomber, and we did not touch or come close to the convoy,” he said. “It seems they are opening fire on civilians intentionally.”

The driver of the bus, Mohammed Nabi, said, “I was going to take the bus off the road.” Then the convoy ahead opened fire.

Like Mr. Mohammed, he said the Americans were about 60 to 70 yards away.

“We were not close enough and we did not violate their signal,” he said. “It is a huge bus full of passengers, and if they think we were a suicide bomber, we are sad that the American have killed innocent people.”

“We don’t feel safe while traveling on the main highways anymore because of NATO convoys,” he said.

The incident came a week after the American-led military command in Kabul— after initial denials of culpability or a cover-up — admitted that its forces had killed three Afghan women during a bungled American Special Operations assault in February.

NATO officials are struggling to contain fallout from a series of tirades against the foreign military presence by the Afghan president, Hamid Karzai, who has also assailed the killing of civilians by Western forces.

Gen. Stanley A. McChrystal, the American and NATO commander in Afghanistan, has had some success in reducing civilian casualties through restrictions on night raids and new controls on Special Operations forces. But mishaps on Special Operations missions — which are blamed for many of the civilian deaths caused by allied forces — continue to anger Afghans.

A statement on April 4 admitted that “international forces” were responsible for the deaths of the women. Officials had earlier said that American Special Operations forces and Afghan troops were involved in the operation. The statement added that “the women were accidentally killed as a result of the joint force firing” at suspects during a house raid.

“We deeply regret the outcome of this operation, accept responsibility for our actions that night, and know that this loss will be felt forever by the families,” said Brig. Gen. Eric Tremblay, a spokesman for the NATO command in Kabul.

In a statement soon after the raid, NATO had claimed that soldiers had come upon the “bodies of three women who had been tied up, gagged and killed” and hidden in the house. Military officials also said later there were puncture and slashing wounds on the bodies, and that the women appeared to have been killed several hours before the raid. – (International Herald Tribune)