Afghanistan's first ever presidential election was thrust into turmoil Saturday after 15 candidates, all opponents of President Hamid Karzai, claimed fraud and asked voting be stopped.

But electoral officials rejected the demand as unjustified. They said despite some technical difficulties, Afghans have turned out in large numbers and the process has been safe and orderly.

The controversy erupted after poll workers at some polling stations mistakenly marked people's thumbs with regular ink meant for ballots. Election officials say the problem was caught quickly and would not affect the overall validity of the vote.

Long lines formed early at polling stations across Afghanistan, as many voters expressed delight at being able to directly choose their leader.