The party is expected to easily form the next government, since it needs only a few more votes in the elected House of Representatives to choose the prime minister under complicated new electoral rules written by the military regime.

Palang Pracharat is expected to be joined by the Democrat and Bhumjaithai parties as well as 11 other smaller parties that are not affiliated with either the pro-army camp or the Democratic Front of parties opposing the military, said Yuttaporn Issarachai, a political scientist from Sukhothai Thammathirat Open University,

"Prayuth will certainly be prime minister," under this scenario, he said, but he added that the government would likely be unstable, with only a slim majority in the House.

Leaders of the Democratic Front have cried foul and threatened legal action, saying both the electoral system and the Election Commission were biased toward extending the military regime.

Election officials and Palang Pracharat deny the accusation.

The Democratic Front of seven parties is led by the Pheu Thai party loyal to exiled former Prime Minister Thaksin Shinawatra, who was ousted in a 2006 coup.

Pro-Thaksin parties had won every election since then but each time saw its governments ousted by legal rulings and coups.

In the latest intervention, the military in 2014 toppled a government that had been led by Thaksin's sister.

It still could be weeks before a new government is formed, even though the pro-junta party is in a favourable position.

Palang Pracharat's most obvious potential allies are the pro-establishment Democrat Party and the Bhumjaithai party, which campaigned on marijuana legalisation among other issues.

The Democrats won 52 seats and Bhumjaithai 51, meaning that either could push Palang Pracharat, which won 115 seats, well over the magic number of 126 votes needed in the House to approve the prime minister under the new system.

The Democrats' spokesman, Thana Chiravinij, told Reuters the party would meet next week to decide whether it would join with Palang Pracharat in government or form an "independent opposition".

But he said the Democrats would never join the Democratic Front because it is led by the pro-Thaksin Pheu Thai. Prominent members of the pro-establishment Democrat Party in 2014 led protests against the civilian government led by Thaksin's sister, with some openly calling for military intervention.

The new post-coup constitution calls for the 250-seat Senate, appointed entirely by the junta, to vote along with the 500-seat elected House of Representatives to choose the prime minister.

Involving the Senate effectively gives pro-army parties a head start of 250 votes to get to the required majority of 376 in the combined House and Senate vote.

By contrast, the Democratic Front has virtually no chance of forming a government thanks to the appointed Senate.

"Thailand isn't returning to democracy," said Titipol Phakdeewanich, dean of the Faculty of Political Science at Ubon Ratchathani University.

"The election was a whitewashing effort for the military to stay in power so that they can tell the international community that they are an elected government," he said.

Australian Associated Press