Afghan authorities faced growing pressure Thursday to open a full anti-fraud probe into the presidential election as EU observers described polling data as "very worrying" and one candidate confirmed he would reject the result.
Abdullah Abdullah, who is reported to be losing the vote count, dismissed plans for a partial audit of the ballots and said he would not accept the outcome due for release Monday -- pitching the election into further turmoil.
The June 14 election run-off has been mired in allegations of cheating, with Abdullah and his poll rival Ashraf Ghani at loggerheads in a dispute that threatens Afghanistan's first democratic transfer of power.
US-led allies who have fought a 13-year war against Taliban militants and spent billions of dollars in aid are eager to avoid a prolonged power struggle in Kabul.
But a risky political stalemate looms at a time when Afghan security forces are taking on the battle against the resilient Taliban insurgency as NATO military forces depart.
The Taliban fired rockets into Kabul international airport on Thursday, destroying President Hamid Karzai's helicopter and damaging three other choppers in an attack that underlined the insurgent threat.
"We will not accept the preliminary results that are to be announced Monday because the fake and clean votes have not been separated," Abdullah's spokesman Baryalai Arsalayee told reporters.
"The process is still not transparent, and massive fraud has not been addressed."
- Fraud sparks international concern -
Abdullah, once a front-runner in the race, alleges he was the victim of "industrial-scale" ballot-box stuffing, with many more votes than voters registered in some areas.
Ghani claims to have won fairly by more than one million votes and accuses Abdullah of refusing to accept defeat -- raising the prospect of a messy election aftermath.
European Union observers on Thursday voiced growing international concern over fraud and called for an audit of suspicious votes to be expanded from 2,000 to 6,000 polling stations -- about a quarter of all ballot boxes.
"I have serious concerns about a significant number of polling stations," EU chief election observer Thijs Berman said.
"I have no conclusions on possible fraud because this you can only do when you have done an in-depth audit, but the indications are very worrying.
"I insist on the necessity to enlarge the audit."
Ghani has complained that the delayed result breaks promises to stick to the election timetable, and has demanded that the preliminary result is revealed on Monday.
Ethnic tensions are rising over the deadlock, according to the UN mission, which pointed to fears of instability as rhetoric between rival supporters sharpens.
"We hope Dr. Abdullah comes back (from his boycott) and establishes relations with the commission again," Ahmad Yousuf Nuristani, the Independent Election Commission chief, said Wednesday.
"It is better to solve issues through negotiations than shedding innocent people's blood to reach power."
Following a period for complaints to be heard, the final election result is now expected on July 24.
With NATO's combat mission ending, the coming months are expected to be a test of the fledging Afghan government forces now responsible for imposing nationwide security.
All foreign combat troops will leave Afghanistan by December, with about 10,000 US troops staying into next year if the new president signs a security deal with Washington.
Any delay in appointing a successor to President Karzai could undermine anti-Taliban operations and also put billions of dollars of aid pledges at risk.