BANGKOK (REUTERS) - A banned Thai opposition party on Sunday (Feb 23) accused the former military junta of helping cover up Malaysia's multibillion-dollar 1MDB scandal, urging Thais to demand the truth ahead of a censure debate against Prime Minister Prayut Chan-o-cha.

The Future Forward Party, the third-largest party in Parliament, was dissolved on Friday by Thailand's Constitutional Court over a loan it took from its billionaire founder.

The dissolution was decried by democracy advocates as a way to weaken opposition to the government of Mr Prayut, who first came to power in a 2014 military coup and led a military junta until after elections last year that his pro-army party won.

Future Forward spokesman Pannika Wanich told reporters at a news conference on Sunday that the junta had worked with Malaysia's former government to arrest a whistleblower in the 1MDB case in 2015 and had allowed financial criminals to operate in Thailand, risking the country's international ties.

"The junta government yearned for international acceptance after the coup...and formed a dark alliance with Malaysia," Ms Pannika said.

"The only person who can issue these orders is Prime Minister Prayut Chan-o-cha," she said.

Ms Pannika cited irregularities surrounding Thailand's arrest and the subsequent confession of Xavier Justo, the Swiss national who was arrested in Thailand in 2015 and the first whistleblower in the 1MDB affair.

The government also harboured Malaysian financier Low Taek Jho, known as Jho Low, allowing him to enter the country at least five times between October 2016 and May 2018, despite Low having an Interpol red notice from Singapore, she said.

Low has been charged in Malaysia and the United States over the alleged theft of US$4.5 billion (S$6.3 billion) from 1Malaysia Development Berhad (1MDB), set up by former Malaysian prime minister Najib Razak with the help of Low, to promote economic development.

At least six countries, including the US, have launched money laundering, financial mismanagement and criminal probes into 1MDB dealings.

Low has denied any wrongdoing. His whereabouts are unknown.

Future Forward Party said it would have opened an investigation on corruption and money laundering related to the 1MDB case if it were in power.

"If we were in government, we would investigate. We want a government that is a responsible neighbour and acts with dignity," Ms Pannika said. "Since we have been dissolved, we can't, but the Thai public can demand the truth."

A spokesman for the Malaysian prime minister's office did not immediately respond to requests for comment.