The country's first democratic transfer of power has been engulfed in fraud allegations, undermining international hopes that a smooth election would help vindicate the costly US-led military and civilian aid effort since 2001.
Abdullah's representatives refused to attend the recount today due to disagreements over how votes would be judged fraudulent or clean -- throwing the election into further chaos.
But a deal was finalised later in the day, averting an imminent collapse of the process to choose President Hamid Karzai's successor as NATO combat troops wind down their 13-year war against the Taliban.
More than eight million votes were cast on June 14, with Abdullah quickly lodging complaints that "industrial-scale" fraud had denied him victory over poll rival Ashraf Ghani.
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The US ambassador in Kabul hailed Abdullah's decision to rejoin the audit as a major step forward, adding that he expected the new Afghan president to be inaugurated at the end of August.
"It is very welcome news," Ambassador James Cunningham said. "A lot of work has been done... So that the audit can go forward at a rapidly accelerated pace in the next couple of days.
The candidates' spokesmen were not immediately available for comment.
The election battle between Abdullah, a former anti-Taliban resistance fighter, and Ghani, an ex-World Bank economist, has threatened to spark a spiral of instability as foreign troops pull out and violence increases nationwide.
After Abdullah rejected preliminary results that named Ghani as the easy winner, US Secretary of State John Kerry flew to Kabul and persuaded the two candidates to agree to the audit to sift out fraudulent votes.
Kerry's intervention quashed growing fears that Abdullah was about to set up a "parallel government", but the UN-supervised audit triggered another outbreak of disagreements.