Kerry, who landed on a pre-dawn, unannounced visit, had earlier said Afghanistan faces a "critical moment" as Abdullah Abdullah and Ashraf Ghani wrangle to take up the reins while international forces withdraw following more than a decade of war.
Preliminary results from a second round run-off have put Ghani in the lead, but Abdullah, who has already once lost a presidential bid, has declared himself the true winner, saying massive fraud robbed him of victory.
Without backing either candidate, Kerry was to meet today with outgoing President Hamid Karzai as well as both presidential hopefuls, UN officials and possibly members of the independent election commission.
He will be pressing both candidates to accept a thorough audit of results in some key areas which have raised concerns.
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The top goal was to try to "finalise the election", a senior US administration official told reporters flying in with Kerry from Beijing.
State Department press office director Jeff Rathke said in a statement that "while the United States does not support an individual candidate, we do support a credible, transparent and inclusive process that affirms the Afghan people's commitment to democracy".
Washington was also looking to the troubled election process to produce "a president who can bring Afghanistan together and govern effectively", Rathke added in the statement.
The United States has warned both candidates that any attempted power grab will lead to an immediate cut in billions of dollars in annual aid to Afghanistan.