By Mirwais Harooni and Maria Golovnina
KABUL, July 7 (Reuters) - Afghanistan declared former World Bank official Ashraf Ghani the winner of last month's presidential election run-off on Monday on preliminary results that threaten to split the country along ethnic lines.
The Independent Election Commission said Ghani won the June 14 second round with 56.44 percent of the vote, according to preliminary results. The tally might still change, however, when the final official numbers come out on July 22.
There was no immediate reaction from Ghani's rival Abdullah Abdullah, a former anti-Taliban resistance fighter who has claimed widespread fraud in the messy vote and insisted results should be delayed until all fraudulent votes were thrown out.
A bloody standoff between ethnic groups or even secession of parts of the country could ensue if he rejects the results.
"The announcement of preliminary results does not mean that the leading candidate is the winner and there is possibly the outcome might change after we inspect complaints," IEC chief Ahmad Yousuf Nuristani told reporters.
The deadlock over the vote has quashed hopes for a smooth transition of power in Afghanistan, a concern for the West as most U.S.-led forces withdraw from the country this year.
Earlier on Monday, rival camps tried to find a last-minute compromise to keep Afghanistan from sliding into a protracted period of uncertainty.
Nuristani said the commission had received a request from Abdullah's camp to review ballot papers from more than 7,000 polling stations on suspicion of fraud - a big enough number which, if recounted, could significantly alter the result.
"We announced preliminary results today and it is now the complaints commission's duty to inspect this case," he said. "We are ready to provide any assistance until the end of the process."
The election was intended to mark the first democratic transfer of power in Afghan history, a crucial step towards stability as NATO prepares to withdraw the bulk of its troops by the end of the year.
Western powers, particularly the United States, had hoped for a trouble-free process that would show that 12 years of their military involvement in Afghanistan were not in vain and contributed to the country's nation-building.
But the process has been fraught with accusations of cheating from the start.
Abdullah, son of a Pashtun father and a Tajik mother, draws much of his support from the Tajik minority in northern Afghanistan. Ghani has strong support from Pashtun tribes in the country's south and east.
Without a unifying leader accepted by all sides, Afghanistan could split into two or more fiefdoms along tribal fault lines, or even return to the bloody civil war of the 1990s.
Abdullah has accused Karzai, also a Pashtun, of playing a role in the alleged rigging in Ghani's favor and says he would accept the vote only if he saw firm evidence that fraudulent votes had been thrown out and the final result was clean.
Taliban insurgents remain a formidable security risk after vowing to disrupt the election process. On Monday, they killed a district police chief in the western city of Herat and attacked a check point in northern Afghanistan. (Writing by Maria Golovnina; Editing by Tom Heneghan)