US Secretary of State Hillary Clinton said on Saturday that a boycott of the run-off election in Afghanistan by runner-up Abdullah Abdullah would not de-legitimise the poll.

Clinton, who was asked whether the outcome of a run-off with only one candidate would result in a legitimate government, said such situations are "not unprecedented" and occur in the United States and other countries.

"We see that happen in our own country where, for whatever combination of reasons, one of the candidates decides not to go forward. I don't think it has anything to do with the legitimacy of the election," she said.

Earlier on Saturday, an official in the Abdullah campaign said the former foreign minister was poised to boycott the run-off unless incumbent Hamid Karzai bows to a series of demands from him.

Following widespread fraud in the August first round, Abdullah has demanded that Karzai sack the head of the Independent Electoral Commission and suspend four ministers who campaigned for the incumbent.

"I'm not going to comment on what any of the candidates might decide to do," Clinton said, adding: "It's a personal choice which may or may not be made."