Kabul:
Afghans head to the polls on Saturday to vote in a second-round presidential election under the threat of Taliban attack, as US-led combat troops wind down a 13-year war that has failed to defeat the insurgents.
The run-off election will decide whether former foreign minister Abdullah Abdullah or ex-World Bank economist Ashraf Ghani leads the country into a new era with declining international military and civilian assistance.
President Hamid Karzai is due to step down after ruling the country since 2001, when a US-led offensive ousted the austere Taliban regime for sheltering Al-Qaeda militants behind the 9/11 attacks.
Afghan officials and international allies are hoping for a repeat of the successful first-round vote in April, when the insurgents failed to launch a single high-profile attack and voter turnout was more than 50 percent.
But the stakes are high with the Taliban issuing specific threats to target polling stations and widespread fears that electoral fraud could produce a contested result.
UN head of mission Jan Kubis issued a stark warning to candidates' supporters not to resort to the kind of ballot-box stuffing that marred the 2009 election when Karzai retained power.
"Do not commit fraud. Do not use intimidation or manipulation to favour your candidate," Kubis said.
Abdullah secured 45 percent of the first-round vote with Ghani on 31.6 percent, after investigations into multiple fraud claims by both sides.
The two candidates came top of an eight-man field, triggering the run-off election as neither reached the 50 percent threshold needed for an outright victory.
A smooth handover in Afghanistan's first democratic transfer of power would be a major achievement for the international effort to establish a functioning state after the depredations of the Taliban era.
The country has seen massive changes as billions of dollars of aid money poured in, bringing rapid development in some cities but only limited improvements in security, women's rights and education.
Long wait for resultsHarsh terrain and poor roads make holding an Afghan election a major challenge, with thousands of donkeys used to transport ballot boxes to remote villages.
Counting the vote will take weeks. The preliminary result is due on July 2 and the final result on July 22.
Ahead of the election, the Taliban said polling booths would be targeted in "non-stop" assaults.
"By holding elections, the Americans want to impose their stooges on the people," the insurgents said on their website.
Police and soldiers have been searching almost every car on the roads of the capital, and Afghan officials expressed confidence in the security forces that have been trained by the US-led military coalition.
"The level of threats is higher compared to the first round," interior minister Omar Daudzai said.
"But we have gained far more experience and we have better equipment and are in a much better position to prevent any possible attack by terrorists."
Ethnic friction is also a concern as Abdullah's support is based among the Tajik minority and other northern tribes, while Ghani is a Pashtun - Afghanistan's largest ethnic group, which is strongest in the Taliban heartlands of the south and east.
Karzai, who is constitutionally barred from a third term in office, has fulfilled his pledge not to interfere in the election - in public at least - though he is tipped to retain an influential role after handing over power.