The chief rival of interim President Hamid Karzai said he has evidence of organized fraud in Afghanistan's election and accused the U.N.-Afghan electoral commission on Monday of ignoring his complaints.

In the second deadly incident surrounding the election, five people — including at least one election worker — were killed by an explosion as they drove near the Pakistan border, the joint U.N.-Afghan electoral commission said.

It was unclear whether the vehicle was targeted or whether they hit unexploded ordnance left over from Afghanistan's long civil war.

Karzai, Afghanistan's stopgap president since the fall of the Taliban in 2001, had captured 62.6 percent of the 1.04 million ballots counted by Monday — about 13 percent of the vote. That put him on course for the simple majority needed to avoid a run-off.

The U.S.-backed incumbent's closest challenger, former Education Minister Yunus Qanooni (search), was trailing with only 17.7 percent. Ethnic Uzbek warlord Abdul Rashid Dostum (search) was third with 9.3 percent.

Ballots so far have been drawn from 29 of Afghanistan's 34 provinces.

Millions of Afghans braved Taliban threats and poor weather to cast their ballots on Oct. 9, an unlikely democratic experiment after a quarter-century of fighting.

Observers and officials have acknowledged problems, especially with ink used to mark people's hands to prevent them voting more than once. A panel of three foreign experts was set up to head off threats by Karzai's 15 opponents to boycott the results.

At a news conference Tuesday, Qanooni said there is evidence of ballot boxes being filled with Karzai votes in at least four provinces: Ghazni, Herat, Zabul and Kunduz. He says his representatives were threatened when they went to check on suspected ballot-box stuffing in Zabul province.

He said he has filed more than 30 written complaints to the U.N.-Afghan electoral commission.

"If his excellency Mr. Karzai, my old friend, succeeds in a fair and transparent election, I will congratulate him and cooperate with him," Qanooni told reporters. "But if the result is fraudulent, the legitimacy of this election will be in question."

Establishing the panel delayed the start of counting, and Qanooni, who served as Karzai's interior and education minister, has forecast that the figures will turn in his favor as more votes are tallied.

Yet four of the five provinces where the count has yet to start are in southern and eastern Afghanistan where Karzai is expected to win. Also, there are no results yet from the 850,000 refugee voters in Iran and Pakistan.

Qanooni also complained that his representatives were unable to monitor ballot boxes during transit from polling stations to counting centers. Organizers acknowledge some boxes arrived with broken seals but say they were damaged by clumsy handling.

"These violations and cheating were organized in advance," Qanooni said.

Sultan Baheen, a spokesman for the electoral commission, rejected Qanooni's charges, saying the candidate's representatives had declined to accompany ballot boxes brought from Iran and Pakistan.

"There is no indication of what the candidates are saying, that boxes have been emptied and refilled," Baheen added. "There's nothing like that."

Few independent observers believe that Qanooni, a member of the ethnic Tajik (search) minority, could command a country deeply fractured by years of tribal and ethnic warfare.

Karzai enjoys strong support among Afghanistan's traditional rulers, the Pashtuns (search), and is seen as a bridge to its international backers and a leader untainted by its bloody past.

Official results are only expected by Oct. 31, but within this week it should be clear who has won the most votes.

Monday's explosion targeted a vehicle of the Joint Electoral Management Body near Yahya Khel, a town in Paktika, a troubled province on the Pakistani border, JEMB spokesman Sultan Baheen said.

One employee of the commission, the driver of the vehicle and three other civilians were killed, he said. All were Afghans.

On election day, three police officers died in a shootout with suspected militants as they escorted a convoy carrying ballot boxes in central Uruzgan province.