With 93 per cent of votes counted late Sunday, the Palang Pracharat party was first with almost 7.6 million votes, according to the Election Commission. Opposition party Pheu Thai, the former governing party ousted by the coup, appeared on course to win the most seats.
The next prime minister needs to win a simple majority in the 500-seat lower house and a 250-seat senate. "These affect the nation's credibility and people's trust", said Sudarat Keyuraphan, Pheu Thai Party's prime ministerial candidate.
Critics have said a new, junta-written electoral system gives a built-in advantage to pro-military parties and appears created to prevent the Thaksin-linked Pheu Thai Party from returning to power.
Speaking to The Straits Times on the phone from Hong Kong on Monday (March 25), Mr Thaksin said he believed both the Thai and global community "know very well (the) irregularity of the result and the irregularity of how the Election Committee of Thailand (ECT) behaved".
Sunday's election followed one of the longest periods of military rule in Thailand, which has a history of elections followed by coups since the end of absolute monarchy in 1932. Unsettled foreign investors have pulled out in excess of a net $700 million from Thai stock and bond markets this year.
He sidestepped questions over wildly inaccurate poll returns reported late Sunday in several constituencies, as down to "human error".
Thailand goes to vote for the first time since the military took power in May of 2014. Pheu Thai, which was the governing party ousted by the coup, was next with 7.1 million votes.
1,862 people here had registered for early voting and 1,542 of them cast their votes, a turnout of more than 80 percent.
"We will ensure that we will do everything according to the mandate of the voters who want us to move the country forward peacefully", he said.
The main opposition party, Pheu Thai, won 7.2 million votes.
Pro-Thaksin parties have won every election since 2001, but the past 15 years have seen crippling street protests both by his opponents and supporters that destabilised governments and hamstrung business.
"This is all knee-jerk reaction", said Maria Lapiz, head of institutional research at Maybank Kim Eng Securities Thailand, adding that Sino-Thai's balance sheets were already strong and would not be affected by the outcome of the election.
Thaksin's aides said he would not answer questions on the royal family, citing the kingdom's lese majeste laws.
In the afternoon the same day, the Election Commission (EC) of Thailand delayed the announcement of preliminary vote result without any reason, saying that it will be announced on March 29.
Thailand has been buffeted by political instability for years. "It will be clearer once the official result is announced", he said.
Although formal ties between Thaksin and Pheu Thai are now legally banned, he amplified the accusations of foul play in an op-ed in The New York Times on Monday.
The Democrats' failure "probably also means that the party is more likely to try to get into a coalition with Palang Pracharat", said Kevin Hewison, a professor emeritus from the University of North Carolina and veteran Thai studies scholar.
Thanathorn Juangroongruangkit, leader of the Future Forward Party, speaks during a news conference at his party headquarters in Bangkok, Thailand, on March 25, 2019.
"Everyone knows in Thailand, everyone worldwide that observed the election in Thailand, knows that (there) is irregularities", he told Agence France-Presse (AFP) in an interview on Monday in Hong Kong. Thai Raksa Chart was forced to disband by the election commission after it nominated the King's older sister, Princess Ubolranata, as prime minister, which was later ruled to be in violation of the constitution.