BANGKOK: Suspended Thai prime minister Prayuth Chan-o-cha is to attend a defence ministry meeting on Thursday as a longtime ally begins his first full day as acting premier and Thailand settled in for weeks of uncertainty while a court ponders Prayuth's future.

Prayuth, 68, retained his cabinet position as defence minister after the Constitutional Court on Wednesday suspended him from the top job pending a review of his constitutionally mandated term limit.

The court decided to hear a petition from the main opposition party arguing that Prayuth, who first came to power in a coup in 2014 when he was army chief, has reached the eight-year term limit because his time as junta chief should count.

The court suspended Prayuth until it delivers a verdict on the petition. It has not given a date. 

Prayuth has made no public comment on the court's decision and it was not clear if he would speak about the matter on Thursday.

A government spokesperson said on Wednesday Prayuth respected the decision and urged the public to do the same, and the government would function as normal.

Deputy Prime Minister Prawit Wongsuwan, 77, also a royalist and ex-army chief with longstanding ties with Prayuth, has taken over as interim leader but was not expected to make a public appearance on Thursday.

Prayuth ruled as head of a military council after he overthrow an elected government in 2014.

He became a civilian prime minister in 2019 following an election held under a 2017 military-drafted constitution in which an eight-year limit for a prime minister was set.

Thailand's next general election is due by May next year.

The controversy over Prayuth's tenure could revive old rivalries at the root of nearly two decades of intermittent political turmoil, including two coups and violent protests, stemming broadly from opposition to military involvement in politics and demands for greater representation as political awareness grows.

'PRAYUTH SHOULD RESIGN'

The main opposition Pheu Thai party, which lodged the petition, was the party forced from power in the 2014 coup, when Prayuth ousted a government led by Yingluck Shinawatra, the sister of former prime minister and telecoms tycoon Thaksin Shinawatra.

Both Yingluck and Thaksin, who was ousted in a 2006 coup, live abroad in self-exile.

The Pheu Thai leader, Chonlanan Srikaew, called for Prayuth to resign.

"For the sake of the country, General Prayuth should resign so we can begin the process of selecting a prime minister based on the constitution as fast as possible," Chonlanan said in a post on Facebook.

Prayuth's supporters argue that his term started in 2017, when a new constitution took effect, or after the 2019 election, meaning that he should be allowed to stay in power until 2025 or 2027, if he retains backing in parliament.

Even if the court later rules Prayuth's term has reached its limit, his ruling coalition has the votes in parliament to choose the next prime minister.

Public reaction to Prayuth's suspension was muted but a small group of pro-democracy activists set off fireworks near the prime minister's residence on Wednesday night and tussled with police.

"Prawit has always been with Prayuth... there is not a lot of differences between them," youth activist Patsaravalee Tanakitvibulpon told Reuters.

"What the regime is doing is swapping the player but the same network remains in power," she said.

Business leaders said the political turmoil may shake investor confidence in Southeast Asia's second-largest economy, the Bangkok Post reported, though adding that the sector was "upbeat".

"No matter what happens to the premier, the business sector remains upbeat that the Thai economy can manage growth," said Sanan Angubolkul, chairman of the Thai Chamber of Commerce.