Afghan and United Nations officials say an explosion in southeastern Afghanistan has killed an election worker and four others, as vote counting continues in the country's landmark presidential election.

A spokesman for Afghanistan's election commission says the victims' vehicle was hit by an explosion as they were driving through Paktika Province.

The dead included an Afghan staff member of the election body and his driver.

U.N. spokesman Manoel de Almeida e Silva says authorities are looking into whether the blast came from a land mine left over from the Afghan civil war, or was a deliberate ambush.

"The area where the incident happened is known for having many mines and many improvised explosive devices, and we do not know which [kind of] explosive material hit the vehicle," he said.

The explosion occurred just more than a week after Afghanistan's first-ever presidential election.

Armed insurgents opposed to the election, including remnants of the former hard-line Taleban regime, had vowed to disrupt the vote, although election day itself was relatively free of violence.

Ballot counting is continuing at regional centers around the country, with a little more than 10 percent of the estimated total tallied.

Early results from the count suggest current transitional President Hamid Karzai was the winner.

The count suggests Mr. Karzai won more than the 50 percent he would need to avoid a run-off election between the top two vote-getters.