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By Hamid Shalizi and Mirwais Harooni
KABUL, April 5 (Reuters) - Voting began on Saturday in Afghanistan's presidential election, which will mark the first democratic transfer of power since the country was tipped into chaos by the fall of the hardline Islamist Taliban regime in 2001.
Taliban insurgents launched a spate of attacks that killed dozens in the run-up to the poll, which they brand a U.S.-backed sham, but there was no word of violence as voting got under way.
"I call on the people of Afghanistan to prove to the enemies of Afghanistan that nothing can stop them," Yousaf Nuristani, chairman of the Independent Election Commission (IEC) told reporters after he cast his own vote in Kabul.
About 12 million are eligible to vote, and there are eight candidates, with former foreign ministers Abdullah Abdullah and Zalmay Rassoul, and former finance minister Ashraf Ghani the favourites.
Hamid Karzai, the incumbent, is not allowed to run for the presidency again by the constitution. But, after 12 years in power, Karzai is widely expected to retain influence through politicians loyal to him.
More than 350,000 Afghan troops have been put on duty to thwart attacks on polling stations and voters. The capital, Kabul, has been sealed off from the rest of the country by rings of roadblocks and checkpoints.
The Taliban have warned civilians they would be targeted if they try to vote, and at least 10 percent of polling stations are expected to be shut due to security threats.
"I am here to vote and I am not afraid of any attacks," said Kabul resident Haji Ramazan as he lined up at a polling station in the capital, which was dampened by a cold drizzle after heavy rain overnight. "This is my right and no one can stop me."
Most foreign observers left Afghanistan in the wake of a deadly attack on a hotel in Kabul last month.
A veteran Associated Press photographer was killed and a senior correspondent of the same news agency was wounded on Friday when a policeman opened fire on the two women in eastern Afghanistan as they reported on preparations for the poll.
RISK OF DELAYED RESULT
Most people expect the election will be better run than the chaotic 2009 vote that handed Karzai a second term amid massive fraud and ballot stuffing.
But it could take months - perhaps until October - for a winner to be declared at a time when the country desperately needs a leader to stem rising violence as foreign troops prepare to leave.
If no one candidate wins over 50 percent, the two with the most votes go into a run-off on May 28, spinning out the process into the holy month of Ramadan when life slows to a crawl.
A long delay would leave little time to complete a pact between Kabul and Washington to keep up to 10,000 U.S. troops in the country beyond 2014, after the bulk of the American force, which currently stands at around 23,500, has pulled out.
Karzai has rejected the agreement, but the three frontrunners to succeed him have pledged to sign it. Without the pact, far weaker Afghan forces would be left on their own to fight the Taliban, who have mounted an increasingly bold and violent campaign against the Kabul government.
Uncertainty over the outcome could also stall crucial foreign aid and economic reform, foment ethnic tensions and leave a political vacuum in which the Taliban could gain ground.
"The whole future of Afghanistan is at stake," Franz-Michael Mellbin, the EU's special representative in Kabul, told Reuters. "It's crucial ... the Afghans come out and vote in large numbers and give political legitimacy, and the aftermath of the elections will be crucial because we need a stable government."
The election is a landmark after 13 years of struggle to quell an insurgency that has claimed the lives of nearly 3,500 members of a U.S.-led coalition of troops and many thousands more from Afghanistan's fledging security forces.
Afghan casualties have been far worse, with at least 16,000 civilians and thousands more soldiers killed in the violence.
Having been backed by the United States from the outset, Karzai's relations with Washington became increasingly strained in later years as Afghan casualties mounted, and frustration grew over a perceived failure to put more pressure on neighboring Pakistan to quell the Taliban insurgency.
Billions of dollars in aid have poured into Afghanistan, bringing fragile gains in infrastructure, education and health to one of the world's most destitute nations. The United States alone has spent more than $90 billion on aid and training Afghan forces.
Although Karzai's departure is a turning point for Afghanistan, none of his would-be successors would bring radical change, Western diplomats say. All three favourites come from the same crop of politicians who built their careers in the early years of Karzai's rule and share similar views.
"The only positive thing in this election is that it is necessary to save the state as it is, and therefore there is a need to transfer power one way or the other," said Sarah Chayes, a South Asia expert at the Carnegie Endowment for International Peace during a media briefing on the eve of the vote.
"Whether the election will be the great transformative event that everybody expects is, I think, delusional."
(Writing by John Chalmers; Editing by Simon Cameron-Moore)