KABUL: Taleban fighters warned Afghans not to take part in the war-wracked country’s upcoming presidential runoff, threatening Saturday 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 insurgents 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 Taleban militants will also cut off key roads and highways and warned that anyone who casts a ballot “will bear responsibility for their actions.”

Taleban fighters killed dozens of civilians during the first round of voting 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 militant-dominated south.

Attacks and fighting have continued amid the electoral crisis. On Saturday, NATO forces announced that two Americans and one service member whose nationality was withheld died in attacks in the south.

Meanwhile, US troops killed four civilians when they fired on a van approaching their convoy on the main highway in southern Kandahar province, according to provincial officials and the US military.

The dead included two women and one child, Kandahar’s governor said in a statement. Four others were wounded, the statement said.

The troops “tried repeatedly to signal the fast-approaching vehicle with passive measures, but fearing for their safety, fired on the vehicle,” said US military spokesman Lt. J.G. Tommy Groves.

NATO expressed its condolences to the families of those who died. Groves said the incident was being investigated and the wounded had been given first aid and taken to a nearby hospital.

A spokesman for Karzai said his campaign is concerned about a spike in violence during the runoff vote, but he said there is no other legal option and ruled out any sort of negotiated power-sharing deal.

“The only legal way to have a legitimate future government is to have elections,” Waheed Omar said. “In our view that is the only constitutional way of putting an end to the current crisis.”

Omar said there is some hope of avoiding a repeat of the violence that marred the August vote, noting assurances from Afghan and international forces that they can provide enough security. He called on the insurgents to let the election go forward without attacks “for the sake of this country.”

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

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