Afghans set to vote in historic presidential election

A massive security operation is under way to thwart the Taliban which has vowed to disrupt the election.Eight candidates are vying to succeed Hamid Karzai, who is barred by the constitution from seeking a third consecutive term as president.The poll has already been overshadowed by the shooting of two journalists.

Award-winning German photographer Anja Niedringhaus was killed and veteran Canadian reporter Kathy Gannon was injured when a police commander opened fire on their car in the eastern town of Khost on Friday. They had both worked for Associated Press for many years.It was the latest in a string of deadly attacks that have marred the lead-up to the election.FrontrunnersThe biggest military operation since the fall of the Taliban in 2001 has been rolled out for Saturday's election, says the BBC's David Loyn in Kabul.Traffic was prevented from entering the Afghan capital from midday on Friday, with police checkpoints erected at every junction.

All 400,000 of the country's police and soldiers have been deployed to provide security for voters attending the polling stations, officials said.International observers are increasingly optimistic that both the tight security and a number of new guarantees against fraud will make this a fairer election than Afghanistan has seen before, our correspondent says.

Afghans have been barred from sending text messages until Saturday evening to prevent the service from being used for last-minute campaigning.But there are still concerns about ballot stuffing and ghost polling stations as well as the fact that the number of election cards in circulation appears to be vastly more than the number of registered voters.

There are eight candidates for president, but three are considered frontrunners - former foreign ministers Abdullah Abdullah and Zalmai Rassoul, and former finance minister Ashraf Ghani Ahmadzai. Dr Abdullah has fought a polished campaign, Dr Ghani has strong support among the new urban youth vote and Dr Rassoul is believed to favoured by Hamid Karzai, our correspondent says.

However, no candidate is expected to secure more than the 50% of the vote needed to be the outright winner, which means there is likely to be a second round run-off on 28 May.

Strong resolveAnja Niedringhaus and Kathy Gannon had been travelling in a convoy with election workers - protected by Afghan security forces - delivering ballots in Khost province when they came under attack.An eyewitness said they were in their own car, waiting to move on from a heavily-guarded compound, when a police commander opened fire on them.

Video of the scene of the attack shows bullet holes in the doors of the car

Ms Niedringhaus, 48, a German photojournalist who was part of a team that won the Pulitzer Prize for coverage of the war in Iraq, was killed instantly.

Canadian-born Kathy Gannon, 60, who had been the AP's bureau chief in Afghanistan for many years and is currently a special correspondent for the region, was shot twice and had surgery. She is said to be in a stable condition.The Afghan interior ministry said it would thoroughly investigate the circumstances of the shooting, but suggested it may have been a case of mistaken identity.The base - close to the border with Pakistan - had been under sustained attack from insurgents for the past 48 hours, spokesman Sidiq Siddiqi said.The run-up to the historic poll has been the bloodiest since the fall of the Taliban, says the BBC's Lyse Doucet.

The heavily-guarded interior ministry, the main compound of the Independent Election Commission and the popular five-star Serena Hotel have all been attacked.

But, says our correspondent, the violence seems to have strengthened the resolve of Afghans to carry on with the election.A poll conducted by the Free and Fair Election Foundation found that more than 75% respondents planned to vote, even though faith in the electoral process was said to be decreasing.

Security forces are a visible presence on the streets of Kabul amid a fear of Taliban attacks on election day

Election staff have had an armed guard as they distributed ballot boxes to polling stations around the country

Associated Press journalists Anja Niedringhaus (left) and Kathy Gannon were accompanying election workers in Khost when they came under attack

Anja Niedringhaus died instantly and Kathy Gannon was badly wounded when their car was attacked by a police unit commander.