By Mirwais Harooni and Maria Golovnina
KABUL (Reuters) - Afghan presidential contender Abdullah Abdullah's camp rejected preliminary results of last month's run-off election on Monday as a "coup" against the people, putting him on a dangerous collision course with his rival, Ashraf Ghani.
The Independent Election Commission on Monday announced that Ghani won the June 14 second round with 56.44 percent of the vote, according to preliminary results. The tally might change when the final official numbers come out on July 22.
Abdullah's camp responded angrily, saying the result was invalid as it did not throw out all the fraudulent votes.
"We don't accept the results which were announced today and we consider this as a coup against people's votes," said Mujib Rahman Rahimi, a spokesman for Abdullah's campaign.
His rejection sets the stage for a possible bloody standoff between ethnic groups or even secession of parts of the fragile country, which is already deeply divided along tribal lines.
Abdullah, a former anti-Taliban resistance fighter, has long alleged widespread fraud in the messy and protracted vote and insisted results should be delayed until all problematic poll stations have been audited.
Son of a Pashtun father and a Tajik mother, he draws much of his support from the Tajik minority in northern Afghanistan and is capable of drawing massive crowds who are likely to be equally enraged by Monday's announcement.
Ghani, for his part, has strong support from Pashtun tribes in the south and east. In the southern city of Kandahar, hundreds of people took to the streets late on Monday to celebrate.
Officials warned this was not the final result, however.
"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 United States echoed the view.
"We have seen today’s announcement of preliminary results and note that these figures are not final or authoritative and may not predict the final outcome, which could still change based on the findings of the Afghan electoral bodies," State Department spokeswoman Jen Psaki said in a statement.
"Serious allegations of fraud have been raised and have yet to be adequately investigated."
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 - which could significantly alter the result if recounted.
"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 vote to pick a successor to Hamid Karzai 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.
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 favour 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 Sonya Hepinstall)