KABUL, Afghanistan – A doctor helping organize Afghan elections died yesterday along with four other civilians when an explosion tore through their vehicle, police said. He was the first election worker to die in violence since the landmark vote.

Meanwhile, interim leader Hamid Karzai consolidated his healthy ballot lead, commanding 61.3% with one-fifth of the votes counted from the October 9 presidential ballot. Election officials may not call the result until the winner is certain but have said the tallies are unlikely to change much once 20% of the votes were counted – a threshold reached yesterday. Mr. Karzai’s closest challenger, the former education minister, Yunus Qanooni, charged yesterday that only cheating had given the American-backed incumbent the advantage. Mr. Qanooni was trailing Mr. Karzai with only 18.8% of the vote.

The explosion destroyed a vehicle of the joint U.N.-Afghan electoral commission in Paktika, a troubled province on the Pakistani border, election spokesman Sultan Baheen said.

Election officials said it was unclear whether the vehicle was deliberately targeted or had struck a mine left over from Afghanistan’s many years of war.

But the local police chief said the car hit a land mine laid on a main road by “the enemies of Afghanistan” – shorthand here for Taliban terrorists, who threatened to disrupt the elections. The police official, Mohammed Rahim Alikhel, identified the election worker as Dr. Sattar, a local physician who had helped organize the vote. The police did not give Dr. Sattar’s full name.

The other victims were the doctor’s nephew, his driver, and two other local men, Mr. Alikhel said.