The comments come less than two weeks after Thailand was shocked by Princess Ubolratana Mahidol announcing she would be the prime ministerial candidate for the Thai Raksa Chart party, an offshoot of Pheu Thai - before King Maha Vajiralongkorn, her brother, stopped that going ahead.

Rumours of a coup that would presumably see the March 24 poll cancelled have also circulated on social media in the last fortnight, although they have come to nothing.

Taken together, Australian National University Thailand expert Greg Raymond, said that "no matter who has the prime ministership after March 24, it's hard to see this being smooth".

Raymond said the reference to Nhak Paen Din from the army chief was an "ominous" sign, but that parties such as Pheu Thai - linked to former prime ministers Thaksin Shinawatra and his sister Yingluck, who were both deposed in separate coups - seemed determined to fight and win the popular vote.

Pheu Thai, Thai Raksa Chart, the newish Future Forward party and other pro-democracy parties were all attracting "moral support from much of the country," Raymond said.

"The tolerance for five years of military rule is coming to an end in Thailand and I think Prayut is aware of that," he said.

In a recent interview with The Sydney Morning Herald and The Age, former deputy prime minister Chaturon Chaisang - who is running for the Pheu Thai-aligned Thai Raksa Chart-  said he did not believe the March poll would be free or fair.

"This is probably the first and only election that will take place under military rule where the junta still have absolute power," he said.

"If you want to resolve the economic problems of this country you need a pro-democracy government, not a military government."

Prayut, who is attempting to win the prime ministership as the candidate for the military-aligned Palang Pracharat Party, has implemented a complicated electoral system designed to make it difficult for any one party to win a majority in the lower house.

Of the 500 spots in the new lower chamber, 350 will belong to MPs directly elected to represent constituencies while 150 will belong to MPs chosen from party lists. The system is weighted to ensure that parties that win more constituency seats will win fewer list seats.

On top of that, 250 senators will be appointed by the military junta.

The next prime minister will therefore need a majority of 376 MPs and senators supporting him or her from the combined 750 people in two chambers.

Chaturon said the new system was therefore unfair, in that it heavily favoured the incumbent.

"If General Prayut can get just 126 MPs to support him, and we believe the 250 senators are likely to vote for him, he can become prime minster," he said.

But Raymond pointed to recent polls that show the junta leader faces a tough test to hang on to power.

"Even the 126 seats Prayut is hoping to get – maybe he won’t even get that."

with agencies