President Hamid Karzai's rival in the second round of the Afghan presidential election has announced in Kabul that he is withdrawing from the poll.
Abdullah Abdullah told the BBC he had made the decision "in the best interests of the country".
Earlier, he told supporters his demands for ensuring a fraud-free election had not been met.
But he stopped short of calling for a boycott of the run-off vote, due to be held next Saturday.
Mr Karzai had rejected Dr Abdullah's demand that election officials who presided over the first round should be dismissed.
BBC's Andrew North, in Kabul
It is almost certain the second round vote planned for 7 November won't happen.
Instead, pressure is mounting on the Afghan election commission to call it off and for the Supreme Court to issue a ruling declaring President Karzai the winner.
Despite calls by some of his supporters for the vote to go ahead, his campaign has now said it will respect any decision by the commission and other legal institutions.
Much of the pressure has been coming from foreign diplomats - the same diplomats in many cases who insisted on a second round to try to restore some legitimacy to the process because of the widespread fraud first time round.
But the United Nations as well as the British, American and other governments with troops here are not prepared to risk their lives for a one-man race.
It will be a deeply unsatisfactory end to the process but at the moment this is seen as the best option. Then will come the decisions on a new Afghan government.
There has been much speculation that there could be some kind of deal which would possibly see the emergence of a national unity government, our correspondent says.
The international community is known to be very reluctant for the run-off to take place.
Instead there is a desire for the legal institutions of Afghanistan to come up with measures to bring the electoral process to an end.
Hundreds of thousands of votes were discounted from August's first round of voting, which was marred by widespread allegations of fraud.
An investigation by the UN-backed Electoral Complaints Commission (ECC) led to Mr Karzai's share of the vote dropping to 49.67% - below the crucial 50% plus one vote threshold needed to avoid a second round.
Karzai camp reacts to Abdullah decision
Dr Abdullah was adjudged in the end to have won about 31% of valid votes cast.
Emotion was clearly visible in Dr Abdullah's face as he announced his decision to pull out of the race to be Afghan leader on Sunday, our correspondent says.
The decision was given to his supporters at a meeting in a big tent in Kabul, where Afghanistan's first post-Taliban government was agreed eight years ago.
Dr Abdullah - a Tajik-Pashtun former eye surgeon - served as foreign minister in the short-lived government headed by the Northern Alliance, and continued as "foreign minister in exile" throughout the years of Taliban rule, which ended in 2001.
He continued in the role in the government that was formed by President Karzai after the fall of the Taliban in 2001, leaving it five years later.
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