Voting was peaceful during the first 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 the Taliban in 2001.

However, four voters were wounded in an explosion at a polling station in the southeastern Logar province, the most serious attack yet in an election that Taliban insurgents had vowed to derail, branding it a US-backed sham.

Police in northern Faryab province said they had arrested a would-be suicide bomber trying to enter a polling station, and in Ghazni, in the southeast, a volley of rockets were fired but landed far from a voting center.

"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 said after voting in Kabul.

About 12 million voters are eligible to choose from the eight candidates, of whom the favorites are former foreign ministers Abdullah Abdullah and Zalmay Rassoul, and former finance minister Ashraf Ghani.

President Hamid Karzai is barred by the Constitution from running again.

More than 350,000 Afghan troops were on duty, guarding against attacks on polling stations and voters. Kabul has been sealed off from the rest of the country by rings of roadblocks and checkpoints.

The Taliban have warned they will target civilians trying to vote, and at least 10 percent of polling stations are expected to be shut due to security threats.

Most foreign observers left Afghanistan following a deadly attack on a hotel in Kabul last month.

Journalists shot

On Friday, veteran Associated Press photographer Anja Niedringhaus, 48, was killed and senior correspondent Kathy Gannon, 60, was wounded when a policeman opened fire on them in eastern Afghanistan as they reported on preparations for the poll.

Gannon has been hospitalized in Kabul and is in stable condition.

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 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 that she expected more to come despite the threat of a Taliban attack.

"We are trying not to think about it, but it's a bit of a concern," she said, only her eyes visible through her black veil.

Risk of delayed result

Most people expect the election will be better run than the 2009 vote, which 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 withdraw.

If no one candidate wins over 50 percent, the two with the most votes will go into a runoff 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 US troops in the country beyond 2014, after the bulk of the US 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.

Reuters-AP