Afghan election commission workers look at a ballot for an audit of the presidential runoff votes at an election commission office in Kabul, Afghanistan, on July 18. (Rahmat Gul/AP)

Election authorities on Wednesday halted the inspection of about 8 million ballots cast in last month’s presidential runoff in Afghanistan, heightening concerns that an already chaotic process to choose the country’s new leader could take months to complete.

The effort to reexamine the votes was paused for a full day to hammer out differences between the two candidates over what criteria to use to scrap suspicious ballots, a spokesman for the Independent Election Commission (IEC) said.

The audit, which began last week, was expected to resume Thursday.

Tensions have been high since the June 15 election, in which former foreign minister Abdullah Abdullah faced off against former World Bank executive Ashraf Ghani after a first round of voting in April in which neither secured the majority needed to win the presidency.

According to preliminary results released by the IEC, Ghani won 56 percent of the vote. Abdullah accused election officials of rigging the vote in favor of Ghani and announced that he was boycotting the IEC. The impasse endangered Afghanistan’s first democratic transfer of power ahead of a scheduled pullout of foreign troops by the end of this year.

U.S. Secretary of State John F. Kerry then flew to Kabul to stave off a full-blown political crisis and clinched an eleventh-hour deal that included a nationwide review of ballots.

But the audit has had a fitful start, marked by fundamental disagreements over what constitutes an invalid vote and which officials make the final decision to discard faulty ballots. Those differences, which emerged before the audit began, came to a head Wednesday after a week of messy recounting.

At the commission’s compound Monday — where all the votes are being audited in large, dark hangars ringed by cement blast walls and barbed wire — the confusion among IEC staffers was clear.

Representatives of the rival campaigns pored over ballots they suspected of being fraudulent, but with no preestablished criteria, decisions — some of them confusing and counterintuitive — were made on an ad hoc basis.

For example, if a voter had signed his or her name next to the candidate’s picture, in lieu of the required check mark, and if the signature was legible, the ballot was deemed fraudulent, international observers there said. But if none of the IEC staff could read the signature, the ballot apparently stayed in. The logic was that a voter could have intended the indecipherable scribble to be a check mark. A legible signature was a deliberate spoiling of the ballot, observers explained.

In another case, during the audit of a box from the Koshanda district of the northern province of Balkh, IEC staffers under the supervision of a U.N. monitor decided that if voters had written any number from one to nine next to a particular candidate’s name on the ballot, the vote would be counted. But double digits indicated fraud. It was unclear why such a decision was made — and it did not appear that IEC officials at other auditing stations were using that benchmark.

The voting in Koshanda district was clearly dubious, international observers said.

“It’s problematic,” Gregory Minjack, a senior adviser with U.S.-based Democracy International’s mission in Afghanistan, said as he observed the audit.

“We haven’t seen anything crazy yet — ghost boxes, the stuff of lore,” he said, referring to reports of ballots that were never dispatched to districts but were simply marked by officials in provincial capitals. NATO-led troops are still transporting ballots from some of the country’s most isolated provinces to the capital.

But once the audit moves on to the eastern and southern regions, where observers anticipate high levels of fraud, “then it’s going to be a problem,” Minjack said. “Then we’re looking at probably one box per day per station.”

Right now 41 teams made up of two IEC auditors — and supplemented by U.N. observers and representatives of each candidates — are auditing an average of six boxes per day, headquarters staff said. More than 23,000 boxes need to be inspected, and as of Monday, just 700 boxes had been completed, a representative from Abdullah’s campaign said.

U.S. and U.N. officials had hoped to finish the audit before September. The presidential inauguration was originally scheduled for Aug. 2, but it has been postponed indefinitely to allow for the recount.

The United States and the international community are worried that prolonging the deadlock could destabilize the country further. As the crisis deepened earlier this month and Abdullah cried foul, his powerful, armed backers threatened to declare a “parallel government.” Afghans worried about a fresh bout of violence.

Abdullah is of mixed Pashtun and Tajik heritage but is backed largely by Tajik populations in the west and the north. Ghani, a Pashtun whose vice presidential candidate is an ethnic Uzbek, draws support from the Pashtun communities in the south and east.

The country’s recent history of internecine warfare — much of it fought along ethnic lines — is casting a shadow over the current crisis. But the two sides are said to have reached an agreement to form a power-sharing government after the recount in which the losing candidate would be awarded a “chief executive” post similar to that of a prime minister.

Afghanistan currently is governed under a highly centralized presidential system. Splitting executive responsibilities will ensure a more even distribution of power and help thwart political and ethnic conflict, U.S. officials said.

Sayed Salahuddin and Mohammad Sharif contributed to this report.