The United Nations said Thursday that a recount of ballots in Afghanistan’s disputed presidential election will take about two more weeks, again delaying the inauguration and adding to the political uncertainty gripping the country.

President Hamid Karzai, who is leaving office after two terms, has already pushed back his departure once this summer and had insisted that he would leave office Tuesday. But a dispute between candidates Ashraf Ghani and Abdullah Abdullah over the outcome of the June runoff remains unresolved and threatens to create further instability.

The U.N. special representative to Afghanistan, Jan Kubis, told Karzai that it will take at least until Sept. 10 to complete the review of more than 8 million ballots. The runoff was held after an initial round of voting in April failed to produce an outright winner, though Abdullah emerged as the top vote-getter in the first round.

The audit is part of a U.S.-brokered agreement to address allegations by Abdullah, who was second in the runoff, that Ghani prevailed because of widespread fraud. The agreement calls for Ghani and Abdullah to form a coalition government once the recount has been completed.

“Mr. Kubis said that a rigorous and credible audit required time,” the United Nations said in a statement. “Following all necessary steps, as required by law, the inauguration of the new president should then be possible soon after.”

An Afghan election worker opens the lock to a ballot box to start counting ballot papers for an audit of the presidential run-off in Kabul August 6, 2014. (Omar Sobhani/Reuters)

U.S. officials had initially hoped that a new president could be in place by midsummer because Karzai has refused to sign an agreement allowing several thousand American troops to remain in Afghanistan after this year. Both Ghani and Abdullah have pledged to sign it.

A delay also means that Afghanistan’s next president will not be able to attend next week’s NATO summit, where the country’s future was to be up for discussion.

Spokesman Aimal Faizi indicated Wednesday that Karzai, who became Afghanistan’s interim leader after the fall of the Taliban government in 2001 and went on to win two presidential elections, is likely to continue serving until a new government is formed.

But the tension between the Abdullah and Ghani campaigns raises doubts about whether they can agree on a unity government.

On Tuesday, Abdullah boycotted the audit, saying it was not sufficiently comprehensive to uncover fraud.

He is now requesting that the results of the recount be withheld from the public until after he and Ghani reach consensus on who assumes what powers in a coalition government, according to two Abdullah advisers.

“Forget about this fraud election, don’t release any results, and let’s talk about the government,” said Khalid Pashtoon, a lawmaker and close Abdullah adviser. “If they release the results, then we go to the zero point, and everything will have to start from scratch.”

Muslim Saadat, a spokesman for Abdullah, said the candidate told U.S. Ambassador James B. Cunningham and Dan Feldman, the U.S. special envoy for Afghanistan and Pakistan, that the audit is not vital to the political process.

“If they continue the audit and they announce a result, it is not acceptable to us,” Saadat said.

But Afghan and U.N. election officials, as well as the Ghani campaign, say the audit’s conclusions should be made public to uphold the legitimacy of the election.

“Our view is that the people’s vote should be respected, and let the process be decided based on the people’s vote,” said Abbas Noya, a Ghani campaign adviser. “Then, based on the announcement, and in light of the constitution, we can start working” on finalizing the setup of the government.

Who would chair cabinet meetings in a unity government and whether there is a role for Abdullah’s two running mates are among the biggest obstacles in the negotiations, according to an Abdullah aide.

Sayed Salahuddin contributed to this report.