(Recasts lede; adds quote from U.S. official, details)
By Lesley Wroughton
KABUL, July 11 (Reuters) - U.S. Secretary of State John Kerry arrived in Afghanistan on Friday for talks in an effort to broker a resolution to a disputed election that threatens to stir up ethnic tensions and undermine a peaceful political transition.
State Department spokesman Jeff Rathke said Kerry would meet with the country's two presidential candidates Abdullah Abdullah and Ashraf Ghani, as well as Afghan President Hamid Karzai and officials from the United Nations.
The Independent Election Commission declared Ghani the winner of the second round of voting on June 14 with 56.44 percent of the vote, a difference of almost a million votes, according to preliminary results. The tally might change when the final official numbers are released on July 22.
Abdullah, who won the first round of voting, rejected the preliminary results as a "coup" against the Afghan people, saying the result was invalid because it did not throw out all the fraudulent votes.
Worried that the country's political transition could be thrown into chaos and fearing a possible power grab, Kerry rushed to Kabul after three days of meetings in Beijing on security, political and economic issues.
Arriving in the early morning hours on Friday, Kerry boarded helicopters to the fortified U.S. Embassy compound where he will meet Abdullah, Ghani and UN officials.
Rathke said Kerry, who has urged both presidential contenders to show leadership at such a critical stage, will press for a thorough review "of all reasonable allegations of fraud," which would entail doing significant additional audits.
"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, and that produces a president who can bring Afghanistan together and govern effectively," Rathke said.
The United believes that the results of the final tally in the second round of voting should not be released until the audits have been completed. Washington considers the results thus far to be preliminary.
Abdullah, the son of a Pashtun father and a Tajik mother, is a former anti-Taliban resistance fighter. Ghani, for his part, has strong support from Pashtun tribes in the south and east.
Kerry has warned that any effort to resolve the dispute through violence or any "extra-constitutional means," would cause the United States to withdraw assistance to Afghanistan.
While the United States is drawing down its military presence in Afghanistan, it provides billions of dollars in aid, which helps to fund the operations of the Afghan government.
A senior State Department official warned that if Washington withdrew support, other donors would likely follow, which would have a significant impact on the Afghan government's ability to succeed going forward.
"This is extraordinarily in the interest of Afghanistan to get this resolved. Both sides have expressed to the secretary that they want to get to an outcome that is credible, transparent and accepting," the official said, speaking on condition of anonymity.
"While we're not coming to impose a solution, but to sort of facilitate that, it is in their interest and expressed desire to get there," said the official, who briefed reporters en route to Kabul. "We're not asking them to do something they don't want themselves." (Reporting by Lesley Wroughton; editing by G Crosse and Peter Cooney)