The blast occurred in eastern Khost province Wednesday as Afghan soldiers were checking the assailant's vehicle, said Mohammed Ayub, the regional police chief. The attacker, sitting in the back seat, detonated explosives hidden under a woman's burqa shroud when soldiers asked to see his ID, he said.

Three Afghan soldiers, the driver of the vehicle and a farmer working nearby were killed, Ayub said. It was not clear whether the driver was an associate of the assailant or an innocent victim. Three soldiers were wounded, as well as a second farmer.

"Apart from the suicide bomber, three national army soldiers were killed," senior provincial police official Mohammad Zaman told reporters.

Taliban guerrillas were believed to be responsible for the attack, he said. There were no casualties among the US troops.

Police initially reported the blast late Wednesday but said it was caused by a land mine and that only two soldiers were killed.

Ayub accused the Taliban of being responsible for the attack.

"The bomber probably wanted to go into Khost city for a suicide attack there, but panicked and blew himself up when the soldiers started checking," he said.

Dozens of people, most of them civilians, have been killed in a wave of attacks -- including 14 suicide bombings -- across Afghanistan's south and east in recent months.

The Taliban, fighting US-led and government troops since being ousted in late 2001, have claimed responsibility for most of the incidents and say they will continue their insurgency until foreign troops withdraw.

The government says the Taliban and their al-Qaeda allies are trying to scare off European Nato members from contributing troops for an expansion of a Nato-led peacekeeping force, while the United States begins to trim the number of its troops in a separate force battling the insurgents.

The Dutch parliament is set to vote on Thursday on whether to send more troops for the Nato force.

The Nato supporter and US ally delayed its decision last year to send up to 1,400 troops, threatening the expansion plan.

The United States has more than 18,000 troops in Afghanistan battling Taliban and al-Qaeda militants and hunting for their leaders.

Under the expansion plan, the 9,000-strong Nato-led force is due to get about 6,000 more troops and move into the dangerous south this year.

Most Afghans say foreign troops are the only way to ensure security until Afghanistan's own security forces are built up.