The leader of Nepal's Maoist party has threatened to boycott parliament if vote counting in this week's "rigged" elections is not immediately halted.
Pushpa Kamal Dahal, better known as Prachanda, alleged that there had been widespread fraud in the polls which amounted to a "conspiracy".
But the Election Commission has rejected his demand.
Early results showed the Maoists trailing in the vote, seen as vital in moving towards political stability.
The vote is the second in Nepal since a 10-year Maoist revolt ended in 2006.
The previous assembly was bitterly divided and failed in its task to draft a new constitution.
It was elected in April 2008 and voted to abolish the monarchy in May of that year.
Addressing supporters in Kathmandu on Thursday, Prachanda said that vote-counting should cease to allow for an immediate investigation.
"We have clearly demanded that there should be a probe of all election processes before the next step," he said.
"If the election commission does not immediately stop counting we will completely boycott the entire election process. We will boycott the Constituent Assembly."
At a press conference he said that he accepted the "people's verdict but cannot accept conspiracy and poll-rigging" because, he said, ballot boxes were tampered with while being transported from polling stations to counting centres.
His boycott warning came after latest poll results showed that the centrist Nepali Congress party was leading in many constituencies across the country, with the Maoists trailing in third place.
Prachanda lost his seat in Kathmandu constituency, but is leading in another seat in the southern district of Siraha.
But Chief Election Commissioner Neel Kantha Upreti told the BBC Nepali Service that counting of the votes would continue even if some politicians boycotted the ballot.
Officials said turnout in Tuesday's election was 70% and voting was largely peaceful, despite sporadic violence on the day and a series of attacks in the run-up to the vote blamed on opponents of the poll.
Foreign observers including former US President Jimmy Carter and the European Union have described the vote as being well conducted.
"The international observers, the domestic observers and all the major parties say it was surprisingly good and fair and already proven to be [a] safe election," Mr Carter told the AFP news agency on Wednesday.
The Maoists won the largest number of votes in the last election, but failed to secure an outright majority.
Prachanda became the country's first post-war prime minister in 2008, but resigned nine months later following a disagreement with the army.
Full results are not due for several weeks. No clear winner is expected.
The Himalayan nation became a republic in 2008, ending 240 years of monarchy.
Five governments have come and gone - two of them headed by the Maoists - since the elections in that year.