By Patpicha Tanakasempipat and Panarat Thepgumpanat
BANGKOK (Reuters) - Two major political parties raised doubts on Monday about the accuracy of Thailand's election results after a party linked to the military took a surprise lead in the popular vote count that suggested the country's junta chief could remain in power.
One party said it was considering a legal challenge over what it said were poll irregularities and, amid popular dismay over the partial results, the number of signatures on an online petition to impeach the Election Commission leapt by more than 300,000 over a few hours to more than half a million.
"There are irregularities in this election that we're not comfortable with. These affect the nation's credibility and people's trust," said Sudarat Keyuraphan, candidate for prime minister of the Pheu Thai Party.
"We've voiced our concerns before for vote-buying, abuse of power, and cheating. All three have manifested. We will fight back through legal means," she told a news conference.
She said her party, which is linked to the military's nemesis, self-exiled former leader Thaksin Shinawatra, would join forces with other anti-junta parties to form a government.
It was far from certain that the military's proxy party would secure enough seats in the 500-seat lower house of parliament for Prayuth Chan-ocha to stay on as prime minister.
Unofficial results of the Southeast Asian nation's first election since a 2014 coup had been expected at 2 p.m. (0700 GMT) on Monday. However, the Election Commission said it would announce only the winners of 350 seats at 4 p.m. (0900 GMT) and a breakdown of votes for those seats would come on Friday.
"We have nothing to hide," the commission's deputy secretary-general, Nat Laosisawakul, told a news conference.
"CHEATING" TRENDS ON TWITTER
With around 94 percent of overall votes counted it appeared that Pheu Thai had fallen far short of expectations, a surprise for many given that Thaksin-allied parties have won every election since 2001. However, it still looked likely to have the largest share of parliamentary seats.
The strong showing by the pro-junta Palang Pracharat Party stunned voters who had hoped the poll would loosen the grip that traditional elites and the military hold on power in a country that has one of the highest measures of inequality in the world.
Amid mounting confusion over the results of the poll, Palang Pracharat's spokesman told reporters his party was aiming to muster 251 of the lower house's seats to form a government.
Many Thais took to social media to voice their suspicions about the results of an election that critics had said was systematically skewed in favor of the military from the outset.
Thai-language hashtags that translated as "Election Commission screw-up" and "cheating the election" were trending on Twitter in Thailand.
Many tweets referred to inconsistencies between the numbers for voter turnout and ballots cast in some parliamentary constituencies. Some questioned the overall turnout of less than 70 percent, which was much lower than expected.
Future Forward, a new party that appears to have made a spectacular election debut thanks to its appeal to young voters, also questioned the poll numbers.
"There are obviously some irregularities with the numbers because they don't add up. This is making people skeptical of the election results," said party spokeswoman Pannika Wanich.
"The Election Commission should address this issue because if the people feel they cannot trust the results, there will be more problems to come," she said.
A change.org petition launched a week ago to impeach the Election Commission had garnered over 511,000 signatures by midafternoon on Monday, up from around 200,000 at the start of the day.
DECK STACKED FOR MILITARY
With all but 6 percent of votes counted, the commission reported that the pro-junta Palang Pracharat was leading with 7.69 million votes. Pheu Thai trailed with 7.23 million votes.
The popular vote numbers did not reflect parliamentary constituency seats won. Pheu Thai could still take the lion's share of these, which are decided on a first-past-the-post basis, because of its popularity in the north and northeast of the country.
Based on a Reuters tally of partial results of the 350 constituency seats contested on Sunday, Pheu Thai was on track to win at least 129 and Palang Pracharat at least 102.
Another 150 "party list" seats in the lower house will be allocated under a complex proportional representation formula.
However, Prayuth looked in a good position to remain in office thanks to a new, junta-devised electoral system.
The lower house and the upper house Senate, whose 250 members are appointed by the junta, will together select the next prime minister.
That means Prayuth's party and allies have to win only 126 seats in the lower house, while Pheu Thai and its potential "democratic front" partners would need 376.
Thailand has been racked for the past 15 years by street protests by both opponents and supporters of Thaksin. The populist former telecoms billionaire was thrown out by the army in 2006 and a government led by his sister was ousted in 2014.