(Adds violent incidents and attempted fraud, colour from Kandahar)
By Hamid Shalizi and Jessica Donati
KABUL/KANDAHAR, Afghanistan, April 5 (Reuters) - Voting was peaceful during the first few hours of Afghanistan's presidential election on Saturday, with only isolated attacks on polling stations as the country embarked on the first democratic transfer of power since the fall of a Taliban regime in 2001.
Four voters were wounded in an explosion at a polling station in the southeastern province of Logar. It was the most serious attack so far on an election that Taliban insurgents had vowed to derail, branding it a U.S.-backed sham.
Police in the northern province of Faryab said they had arrested a would-be suicide bomber trying to enter a polling station, while in Ghazni, in the southeast, a volley of rockets were fired but landed far from a voting centre.
"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) said after he had cast his own vote as a polling station opened 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 barred by the constitution from running for the presidency again. But, after 12 years in power, he is widely expected to retain influence through politicians loyal to him.
More than 350,000 Afghan troops were on duty, guarding against 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.
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.
The National Directorate of Security intelligence agency said it had arrested a man and seized a cache of rocket-propelled grenades, assault rifles and police uniforms from a house in Kabul hours before the election began.
In the city of Kandahar, cradle of the Taliban insurgency, the mood was tense. Vehicles were not allowed to move on the roads and checkpoints were set up at every intersection.
Hamida, a 20-year-old teacher working at a Kandahar polling station, said more than a dozen women turned up in the first two hours of voting and added that she expected more to come despite the threat of an attack by the Taliban.
"We are trying not to think about it, but it's a bit of a concern," she said, only her honey-brown eyes visible through her black niqab.
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.
The interior ministry said two officials were detained on Saturday for trying to rig the vote, and elsewhere several people were arrested for trying to use fake voter cards.
Even if the election is less flawed than 2009, it could take months - perhaps even 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 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. 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 neighbouring Pakistan to quell the Taliban insurgency.
Billions of dollars in aid have poured in, 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.
"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," Sarah Chayes, a South Asia expert at the Carnegie Endowment for International Peace told 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."
(Additional reporting by Mirwais Harooni in KABUL; Writing by John Chalmers; Editing by Simon Cameron-Moore)