Seven political parties formed a coalition in Thailand on Wednesday, vowing to thwart a military-backed proxy in a bid to end years of junta rule following the country's first election since a 2014 coup.
A junta-aligned party and its main rival have both claimed the right to govern the country after Sunday's vote, prompting a political standoff.
Questions over irregularities are swirling following invalidated ballots and accusations of skewed numbers, with a fully tally of official results not expected to be confirmed for several weeks.
The Pheu Thai party, affiliated with self-exiled former premier Thaksin Shinawatra, joined forces with six other parties in a bid to halt military-backed factions from staying in government.
"We want to stop the regime from hanging onto power," Pheu Thai's prime ministerial candidate Sudarat Keyuraphan told reporters.
"Pro-democracy parties received the most trust and consensus by the people," she added, conceding that final results have not yet been released.
Thailand has been ruled by a junta since a 2014 putsch led by general Prayut Chan-O-Cha, the prime ministerial candidate for the Phalang Pracharat Party.
His party stunned the pro-democracy camp by winning the popular vote on Sunday with 7.6 million ballots, according to preliminary results.
Its main rival Pheu Thai got 400,000 fewer votes, but is now aiming to take the majority of seats in the lower house with its newly-formed coalition.
The seven-party bloc claimed it would take 255 out of the 500 lower house seats that are up for grabs, but with all official results not expected until May 9 the numbers are not ironclad.
But the party still cannot elect a prime minister without commanding at least half of all 750 seats in the lower and upper houses.
The balance of power is stacked in the junta's favour thanks to a charter it drafted creating 250 military-appointed upper house seats.
That means non-military parties like Pheu Thai need an avalanche of votes in order to elect a prime minister.
The coalition formed Wednesday does not include two other high-profile parties -- Bhumjaithai and the Democrat Party -- who together have around 70 seats so far and whose allegiances are still up for grabs, with Phalang Pracharat expected to seek its own allied bloc.
Sunday's election had been repeatedly delayed and was seen as a test for Thailand's tattered democracy, which has seen at least 12 coups since 1932.
The junta-backed Phalang Pracharat party did better than expected by clinching the most popular votes.
"This is the people's mandate who want Prayut to become prime minister," said party deputy spokesman Phalang Pracharat.
Weeks of messy negotiations and vote tallying are now expected before the final outcome is confirmed.
Even as the coalition sought to create a united "democratic front", it will be almost impossible for them to get the votes they need to elect a Prime Minister, said Aaron Connelly, Singapore-based research fellow at the Institute for International and Strategic Studies.
They "seem to be laying down a marker, claiming the legitimacy to oppose the junta in the next parliament", he told AFP.
Initial results have been plagued by controversy after the Election Commission unexpectedly said it would delay the final count.
The head of Future Forward, a newly-formed party that targeted first-time millennial voters, urged a swift count of votes across the country.
"We are calling for the Election Commission to perform its duty in a free and fair manner," the party's telegenic billionaire leader Thanathorn Juangroongruangkit said Wednesday after joining the coalition.
Britain and the US have also called for irregularities to be investigated.
"We stand with the Thai people in calling for the expeditious announcement of voting results and a fair and transparent investigation of any reported irregularities," US State Department spokesman Robert Palladino said in a statement.