Faced with over a month's wait before the full results of Sunday's general election are in, Thailand's top-performing political rivals dug in their heels yesterday as they both insisted they had the mandate to form a government.

The Pheu Thai Party, which won the most constituencies, declared that parties opposing the ruling junta already had a majority in the 500-seat Lower House and won six million more votes than the faction trying to return Prime Minister Prayut Chan-o-cha to the premier's post.

Pro-junta Palang Pracharath insisted that it will form the government because it had won the highest number of votes.

"Any party that gets the most votes will form the government, and we are confident that we can do that," its secretary-general Sontirat Sontijirawong said yesterday. He promised that the government would be formed soon.

"We just need some time to talk," he said, referring to talks with other parties to form a coalition.

Mr Prayut, who staged the 2014 coup that ousted the then Pheu Thai government, stayed above the fray.

"I don't have anything to do with the forming of government," Mr Prayut told reporters at the Government House, while saying that he respected the vote of every person who cast a ballot.

"I will go on with my job as Prime Minister, as the leader of the National Council for Peace and Order (NCPO) and the government, to run everything - including the royal coronation - well." NCPO is the name for the ruling junta.

Meanwhile, Thailand's King Maha Vajiralongkorn will be officially crowned in a grand ceremony from May 4 to 6, some three years after assuming the throne.

The monarch - through a statement issued by the palace on the eve of the landmark election - had urged Thais to support "good people".

Coming eight years after the last general election, Sunday's poll was marred by allegations of fraud and mismanagement. Poll monitoring group Asian Network for Free Elections (Anfrel) said yesterday that deeply flawed tabulation and consolidation of ballots led to the release of wildly inaccurate preliminary results on Sunday.

"The blunders did further damage to the perceived integrity of the general election, and Anfrel invites the (Election Commission) to release comprehensive election results as soon as possible in order to foster trust in the general public's eye."

However, the group said it was too early to tell if there had been genuine electoral fraud despite allegations by fugitive former prime minister Thaksin Shinawatra that the polls were rigged. Pheu Thai belongs to a Thaksin-linked faction that has won every election since 2001.

The new Constitution gives the NCPO leverage over the future Parliament through a 250-member Senate largely appointed by the junta.

As the Senate has to vote on the choice of prime minister with the 500-seat Lower House, Palang Pracharath would technically need only 126 Lower House seats to push Mr Prayut's nomination through.

But such a scenario creates a precarious minority government, so Palang Pracharath is expected to try to stitch together a coalition with at least 251 Lower House seats.

Pheu Thai appears to have staked its claim first, and will hold a media conference today together with parties that it said are "on the side of democracy".

Secretary-general Phumtham Wechayachai said: "Despite using all their powers and state mechanisms to manipulate this election, they cannot get the majority of votes in Parliament. The majority in fact oppose General Prayut being the next prime minister."

The Election Commission has said it will take up to May 9 to release the full results.

So far, it has disclosed only a list of preliminary winners among the 350 constituency seats contested, without details on the winning margins.

There is no information about another list of 150 Lower House seats, which need to be allocated according to the proportion of the national vote won by each party.

According to the commission, Pheu Thai won 137 seats and Palang Pracharath 97. Behind them are the Bhumjaithai Party with 39 and the Democrat Party with 33. Both are seen as likely coalition partners of Palang Pracharath.

The Future Forward Party, which won 30 seats, has already declared its intention to join forces with Pheu Thai.

Meanwhile, it is estimated that Palang Pracharath has garnered 500,000 more votes nationwide than Pheu Thai.