KABUL — Taliban fighters warned Afghans not to take part in the war-wracked country's upcoming presidential runoff, threatening today to launch a fresh wave of violence on polling day to stop them.

The warnings came on the first official day of campaigning for the Nov. 7 vote. The militant group denounced the race between President Hamid Karzai and challenger Abdullah Abdullah as "a failed, American process" and said its fighters would "launch operations against the enemy and stop people from taking part."

The statement said Taliban militants also will cut off key roads and highways, and warned that anyone who casts a ballot "will bear responsibility for their actions."

Taliban fighters already killed dozens of civilians during the first round of voting on Aug. 20, barraging several southern cities with rocket-fire and cutting off the ink-stained fingers of at least two people who cast ballots in the south.

Security fears are just one of the challenges election officials face as they scramble to organize a new election amid a swelling Taliban insurgency before the advent of winter, which begins around much of the country around the middle of November, isolating remote villages and cutting off roads with snow.

As campaigning began today, several senior Abdullah campaign officials accused the top three members of Afghanistan's Independent Election Commission of bias, saying they should be replaced to ensure the country's upcoming runoff is fair.

A spokesman for the commission, Noor Mohammad Noor, denied the allegations and said it was "impossible" to replace them.

Under intense U.S. pressure, Karzai acknowledged last week that he fell short of the 50 percent threshold needed for victory in the August ballot after U.N.-backed auditors threw out nearly a third of his votes because of massive fraud.

The Afghan Independent Election Commission, dominated by Karzai supporters, is under huge pressure to avoid a repeat of the cheating, which discredited the government and threatened to undermine public support in the United States, which provides the bulk of the 100,000 NATO-led force.

Abdullah officials singled out election commission chairman Azizullah Lodin, chief electoral officer Daoud Ali Najafi, and the commission's deputy director, Zekria Barakzai. Abdullah's running mate, Homayoun Assefy, said the three were "openly working for Mr. Karzai" and should resign.

"If they are again in charge for the second round, the same thing will happen," Assefy said, referring to the widespread fraud. "If the second round is also controversial, then the result will not be good."

Assefy said the campaign was putting together a list of changes it would like to see in the runoff, including the changes at the top of the election commission.

"If none of our conditions are met, it will be sort of a boycott," he said, without elaborating.

Noor said the officials had been appointed by constitutional procedures and cannot be replaced.