Col. Thomas Collins, a coalition spokesman, voiced regret for any deaths and injuries. He said a large cargo truck in a coalition convoy had suffered a mechanical failure and hit as many as 12 civilian vehicles at a busy intersection. He said the coalition was conducting an investigation.

He confirmed there was gunfire at the scene, and that coalition personnel in one military vehicle had fired over the crowd.

"This was a tragic incident and we deeply regret any deaths or injuries resulting from this incident," Collins in a statement. "We will determine the facts regarding the incident and cooperate fully with Afghan authorities."

The U.S.-led coalition said at least one person was killed and six injured in the crash. Afghan Health Ministry spokesman Abdullah Fahim said five bodies were brought to hospitals in Kabul and 60 more Afghans were treated for injuries.

He said there were no foreigners among the wounded or dead. He had no details on how the casualties occurred, and it wasn't immediately clear if the toll included people from the traffic accident.

Witnesses said the incident began when a convoy of at least three U.S. Humvees came into the city from the outskirts and hit several civilian cars in rush-hour traffic jam.

"The American convoy hit all the vehicles which were in their way. They didn't care about the civilians at all," said Mohammad Wali, 21, a shopkeeper.

Three people were killed and 16 wounded in the crash, said Sher Shah Usafi, a Kabul police chief. U.S. forces then fired on the crowd, killing one person and wounding two, he said.

A commander with the city's traffic police who was at the scene said he also saw U.S. forces firing on protesters. He spoke on condition of anonymity because he was not authorized to speak to the media.

AP Television News video showed hundreds of angry young men hurling rocks at what appeared to be three U.S. military trucks and three Humvees as they sped from the area after the crash, their windscreens cracked by the stones.

A center-mounted machine gun on one of the Humvees was seen firing into the air over the crowd as the vehicle sped away. The video also showed an Afghan man apparently hurt in the riots lying on the ground, being comforted by others around him.

An AP reporter said he saw about 10 Afghan police firing into a crowd of about 50 demonstrators, and that U.S. troops had already left the area. The protesters scattered when the firing erupted, but later regrouped.

Two helicopters belonging to a NATO-led peacekeeping force hovered over the area.

Phones in Kabul were only working sporadically. Repeated attempts to get through to the city's hospitals to get a casualty toll from the unrest were unsuccessful.

State television cut transmission of a live broadcast of parliament when one angry lawmaker interrupted the proceedings to protest the incident.

"I have seen the incident. ... I come from that area and I have to tell you," Taj Mohammed Mujahid shouted before the house speaker ruled him out of order and the screen went black.

Transmission resumed minutes later and parliamentary speaker Yunus Qanooni called for calm.

"We call on the people to be tolerant because there is the risk this could be exploited by our enemies," he said, referring to Taliban rebels who are waging a fierce insurgency in the country's southern and eastern regions.

He said the Cabinet was discussing the matter.

Afghans often complain about what they call the aggressive driving tactics of the U.S. military. Convoys often pass through crowded areas at high speeds and sometimes disregard road rules. The U.S. military says such tactics are necessary to protect troops from attack.