Afghan presidential candidate Abdullah Abdullah, second from right, arrives for an election rally in central Bamiyan province on Wednesday. (Ahmad Masood/Reuters)

The Taliban urged Afghans on Thursday to stay away from the Aug. 20 elections, threatening to block the roads to polling stations and dismissing the balloting as an "American process."

In a statement posted on a website used frequently by the militants, the extremist Islamic movement mocked the upcoming presidential and provincial polls as part of an American "failed strategy" in the country — paid for and secured by foreigners.

The statement highlights the pressure likely to face voters who choose to cast ballots in areas of the country where the insurgents are strongest.

"All those Afghans should stand together with the Islamic emirate and should not participate in this American process," the Taliban said in a statement. The Islamic emirate is the name used by Taliban groups loyal to Mullah Omar.

The statement urged Taliban fighters to prevent people from voting.

It said that a day before the elections, roads would be blocked to government vehicles and civilian traffic "and the people should be aware of that."

Low turnout could throw results into question

Hundreds of polling stations are likely to remain shut on the election date, almost all in areas dominated by Pashtuns, the biggest ethnic group and the backbone of the Taliban. A low Pashtun turnout could call the legitimacy of the election results into question.

A low turnout in Pashtun areas could also cost President Hamid Karzai support among his fellow Pashtuns, who tend to vote by ethnicity even though many of them are disenchanted with him because of his ties to the Americans.

Karzai's chief rival in the 39-candidate field, former Foreign Minister Abdullah Abdullah, is popular in northern Tajik areas, which are more peaceful and more likely to have a strong turnout.

Karzai is widely assumed to be the front-runner but if he fails to win more than half the votes in the crowded field, he would face a runoff with the second-place finisher in October. Karzai could be vulnerable if his opponents rally around an alternative candidate in the runoff.

It was unclear whether the Taliban would be capable of intimidating large numbers of people from voting.

Ronald Neumann, the former U.S. ambassador to Afghanistan, said the Taliban had tried to stop the 2004 presidential election but had failed.

"There will obviously be some danger if the Taliban really try to stop the voting but in my experience if people really want to vote they will do so," Neumann said.