The chief political challenger to Afghan President Hamid Karzai has announced he is withdrawing from the forthcoming run-off election. Abdullah Abdullah polled second behind Karzai in the election on August 20, the results of which were subsequently scrapped because of claims of voting irregularities. He said he would not be participating in next weekend's ballot because his demands for measures to prevent fraud this time around were rejected. Asked by reporters if he was calling upon his supporters to boycott the election, Abdullah said: "I have not made that call." His running mate, Homayoun Assefy, added that it was up to the government's Independent Election Commission to decide whether to hold the run-off next Saturday as scheduled. Karzai campaign spokesman, Waheed Omar, called Abdullah's withdrawal from the race "very unfortunate" but insisted that the ballot should proceed without him. "Our stand is that the election is the right of the Afghan people. The withdrawal was Dr Abdullah's personal choice. That should not affect the process as a whole," Omar said. In an emotional speech, Abdullah said that he did not believe a free and fair election was possible without changes in the leadership of the electoral commission, which ran the first-round ballot. A run-off was ordered after UN auditors threw out nearly a third of Karzai's votes in the first round ballot, dropping him below the 50 per cent threshold for victory in the 36-candidate field.