“The damage of fraud and suicide bombing is the same to the people of Afghanistan,” he said.

This is the third time Mr. Abdullah has disputed election results after running for president.

A similar dispute between Mr. Abdullah and Mr. Ghani in 2014 went to a messy stalemate that was resolved through a power-sharing agreement brokered by John Kerry, then secretary of state. That arrangement made Mr. Ghani president and Mr. Abdullah the chief executive. This time around, with American diplomacy focused on negotiating an end to the war with the Taliban, American officials and other Western allies have made clear they will not step in to mediate.

The dispute is playing out as the United States continues negotiations with the Taliban to seek an end to the long war. In the fall, just as the two sides seemed on verge of a deal that would open way for Taliban negotiations with Afghans over power sharing, the election seemed unlikely. But when president Trump called off the talks with the Taliban, the Afghan the vote went ahead.

A political crisis, or a bruising runoff if the vote goes to that, could weaken the Afghan government’s hand in any negotiations with the Taliban. An extended political crisis could also undermine military efforts against militants seeking to demonstrate that the government cannot protect its citizens.

The announcement of preliminary results came after weeks of tense discussions to find a compromise between the grievances of Mr. Abdullah’s supporters and the position of the election commission.

Among the roughly 300,000 votes Mr. Abdullah disputes are 100,000 ballots registered in the system either before or after voting hours — in some cases by weeks or months. The election commission attributes the irregularities to human error in setting the time and date of devices that recorded the votes.

Last week, as expectations grew that the election commission would announce initial results, Mr. Abdullah made a concession by calling on his supporters to allow the audit of the seven provinces they were blocking. He described it as a good will gesture to get the commission to reconsider its decision on the nearly 300,000 questionable votes. But the election commission did not budge.