Under a proposal put forward by the United Nations, the country's elections commission would audit ballot boxes from just over 8,000 polling stations where suspicions have been raised about the vote count.
The bitter standoff between Abdullah Abdullah and Ashraf Ghani over the run-off vote to succeed President Hamid Karzai has plunged Afghanistan into crisis and raised fears of a return to the ethnic violence of the 1990s.
"They are neither authoritative nor final, and no-one should be stating a victory at this point in time," Kerry said, as he held back-to-back meetings in the heavily-fortified US embassy after arriving in the early hours.
"We want a unified, stable, democratic Afghanistan. It is important that whoever is president is recognised by the people as having become president through a legitimate process," he said.
Also Read
Despite Monday's announcement, Abdullah, who has already lost one presidential bid in controversial circumstances, has declared himself the true winner, saying massive fraud robbed him of victory in the June 14 run-off vote.
"Our commitment is to ensure that the election process enjoys the integrity and the legitimacy of the people of Afghanistan and the world," Ghani told reporters as the two men met.
"Therefore we believe in the most intensive and extensive audit possible to restore faith."
UN officials late yesterday presented a plan to outgoing Karzai to audit polling stations across 34 provinces.
These would be selected according to five criteria that could indicate voting fraud -- such as whether the results were multiples of 50, or where women's polling stations were staffed by men.