An AFP reporter saw around seven bullet-riddled vehicles, some smeared with blood, at the site of the attack on the main road between Kabul and Pakistan in the eastern province of Nangarhar.

A few thousand demonstrators gathered afterwards to protest the killings and blocked the road, about 50km from the city of Jalalabad in the Marko area, for several hours, witnesses said.

Reports said demonstrators chanted "Death to America" and "Death to (President Hamid) Karzai".

There were conflicting reports about the death toll. Provincial police spokesman Ghafoor Khan said 16 people were killed and between 25 and 30 wounded, while a district official said six were dead.

The US-led coalition force, which has US troops in the area, confirmed a patrol had been struck by a suicide car bomb. It could not give further details.

The coalition did not give information about casualties.

An AFP reporter at the scene saw the decapitated body of a person who appeared to have been killed in the suicide blast, but authorities did not release a casualty toll for the explosion. The vehicle used in the bombing was destroyed.

Photographers told AFP that US soldiers who cordoned off the area had taken their cameras and deleted pictures taken at the site.

A spokesman for the interior ministry, Zemarai Bashary, told AFP that casualty figures from the bombing and shootout were being confirmed. "Our forces have gone to the area," he said in Kabul.

There have been several incidents in Afghanistan in the past weeks in which foreign soldiers have opened fire on civilians fearing suicide or other attacks by Taliban militants.

Insurgent commanders have vowed a new wave of suicide attacks this year as part of their al-Qaeda-style campaign against the US-backed government that was installed after the Taliban regime was toppled in 2001.

Elsewhere, the Nato-led International Security Assistance Force (Isaf) reported that two of its soldiers were killed Saturday in combat in the south of the country, which sees the most violence linked to a Taliban insurgency.

The 37-nation Isaf gave no details of the killing of its two soldiers in the south, leaving this announcement to the home country.

Twenty foreign soldiers have now been killed in Afghanistan this year, most of them in the volatile south of the country.

Two -- an American and a South Korean -- were killed on Tuesday in a suicide bombing outside a military base being visited by US Vice President Dick Cheney.

In other violence linked to the insurgency, one Taliban fighter was killed and three wounded in the southern province of Nimroz late Saturday, the provincial governor, Ghulam Dastgir Azad, said. Seven others were arrested.

Another Taliban was killed and three wounded in an attack in Zabul province, a provincial security chief said. (AFP, AP)