Afghan election commission workers sort ballots for an audit of the presidential runoff votes at an election commission office in Kabul on Monday. (Rahmat Gul/Associated Press)

Afghanistan’s election crisis continued to deepen Tuesday as the campaign of second-place candidate Abdullah Abdullah warned that it will abandon a U.S.-brokered deal to end a political stalemate unless major changes are made in how millions of votes are being reexamined.

Abdullah adviser Fazal Ahmad Manawi said the candidate has serious concerns that an ongoing audit of more than 8 million votes cast in a June runoff is not stringent enough to catch fraudulent ballots. He called the audit a “joke” and said new procedures must be implemented by Wednesday or Abdullah could walk away from the recount.

“If by tomorrow morning our demands . . . are not accepted, our patience has ultimately run out,” said Manawi, who has been who was tasked by Abdullah with monitoring the recount. “We will consider this process a finished one, will not continue in it and not accept it, and the results will have no value to us.”

The tension comes as the Independent Election Commission of Afghanistan and international observers race to complete the audit, which was expected to result in the election of only the second Afghan president since U.S.-backed Afghan forces drove the Taliban from power in 2001. The process has taken on more urgency in recent days because outgoing President Hamid Karzai has stressed that he is leaving office in one week and expects his successor to be inaugurated next Tuesday.

Abdullah is a former foreign minister and top aide to legendary Afghan guerrilla commander Ahmed Shah Massoud, who was assassinated by al-Qaeda operatives two days before the Sept. 11, 2001, attacks. Abdullah finished first in a field of eight candidates in the initial round of voting in April but fell short of a majority, necessitating the runoff with former finance minister Ashraf Ghani, who finished second.

Preliminary results from the runoff that were released last month showed Ghani leading by a substantial margin, prompting Abdullah to allege widespread fraud and demand a recount.

This month, Secretary of State John F. Kerry traveled to Kabul and brokered an agreement that called for an audit of the ballots and the formation of a unity government once the results of the recount are announced. On Friday, President Obama called the candidates and urged them to respect the agreement.

A spokesman for Ghani said he remains optimistic that the candidates, who met Tuesday night, can work out their differences. He declined to respond to Manawi, saying he suspects that Abdullah advisers are divided over tactics.

But some senior Ghani advisers are growing increasingly frustrated by what they view as threats from the Abdullah campaign.

Daoud Sultanzoy, a former presidential candidate who is now a top aide to Ghani, said that there was probably “fraud on both sides to some extent” and that that is “why we have an audit.” Threatening to pull out of the process, he said, is “selfish and egotistical.”

“If they don’t show up, so what,” Sultanzoy said of the Abdullah campaign. “The international community gives them too much credence. Their pacifier falls out and they start crying. We should be tough, and people who threaten the stability in this country, we should not accommodate them.”

After the runoff, Abdullah’s allegations of fraud led to considerable tension and fears of civil unrest. That complicated the Obama administration’s efforts to forge a long-term security agreement to allow several thousand U.S. troops to remain in Afghanistan after most other NATO forces withdraw this year.

Concerns about violence were heightened by an apparent split among voters along ethnic lines. Ghani, who is Pashtun, received his greatest support among Pashtuns, Afghanistan’s largest ethnic group. Abdullah’s mother is of Tajik descent and his father was Pashtun, but Abdullah appeared to receive most of his support from predominantly Tajik areas of northern Afghanistan, where Massoud, his late mentor and an ethnic Tajik, was especially revered.

In a statement Tuesday, the United Nations said it is reviewing Abdullah’s concerns and will “continue to work with both campaigns” to refine the recount process. But it stressed that the audit will continue even if Abdullah withdraws his support.

“Should one campaign choose not to participate in the conclusion of the enormous exercise which they requested, the United Nations and the domestic and international observers will increase their participation so as to ensure the continuing credibility of the process,” the statement said.

Most observers doubt that the audit will result in an Abdullah victory. But observers and U.S. diplomats were hopeful that Ghani and Abdullah could reach a deal on forming a coalition government.

The two sides have struggled, however, to agree on what roles the first- and second-place finishers would play in such a government.

Any decision by Abdullah to withdraw from the audit process would again raise fears of clashes between the candidates’ supporters. In a recent interview with The Washington Post, Attah Mohammed Noor, an Abdullah ally and longtime governor of Balkh province, warned that he would lead a “civil uprising” if the process was biased against Abdullah.

“We will not be responsible for whatever its aftermath may be,” Manawi said Tuesday. “Those who have cheated us in recent weeks and have not accepted our logical views will bear the responsibility.”

Sultanzoy countered by accusing some Abdullah supporters of “being reckless” in suggesting that an election outcome that is not in their favor could lead to violence. But if such a scenario plays out, he said, Ghani supporters will be prepared to handle it.

“On the day of the election, those who voted for Dr. Ghani left their guns at home and came and voted. Our votes meant peace,” Sultanzoy said. “And the same people who came and produced peace on the day of the election, don’t you think they can quell hooligans and uprisings that cause damage to our national interests?”

Sayed Salahuddin and Sharif Hassan contributed to this report.