Qanuni and 14 other challengers to Karzai had earlier announced a boycott of last Saturday's vote, saying the system to prevent multiple voting had failed.
The Afghan-United Nations election management body has announced that a panel will investigate irregularities in the vote, and has asked candidates to submit any complaints by this evening.
UN Secretary-General Kofi Annan welcomed what he called the "enthusiastic voter turnout" in the election and said in a statement that the vote gives Afghans an historic opportunity to establish a democratic nation.
(AP/Reuters/AFP)