US President Donald Trump will host Thai junta chief Prayut Chan-O-Cha at the White House next Tuesday, in a personal triumph for a Thai autocrat who was shunned by Barack Obama's administration for his regime's dismal rights record. 

Ties between the long-time allies were strained by Prayut's 2014 military coup, which ushered in the former democracy's most authoritarian government for a generation.

But Trump's administration has started to reset relations with the junta government, dispatching  high-level diplomats including the secretary of state, whose predecessors under Obama had noticeably avoided the kingdom in the wake of the coup. 

"President Trump looks forward to reaffirming the relationship between the United States and a key partner and longstanding ally in Asia, the Kingdom of Thailand," the White House said in a statement late Monday.

Speaking to reporters in Bangkok on Tuesday, Prayut said the two leaders would discuss "security, trade and investment, and regional problems", adding that he expected the talks to be held in a "cordial climate". 

Human Rights Watch lambasted the October 3 visit, which follows an invitation Trump extended during an April phone call, as the latest sign that the US president has "shamelessly thrown human rights considerations out the window".

"Doubtless Trump fails to realise that this propaganda victory for Prayut and the junta will come at the expense of the people of Thailand, who will pay for it in the form of intensified repression and human rights abuses when the general gets home," said HRW's Asia director Brad Adams.

- 'Not taking sides' -

Thailand's military has suspended democracy for more than three years, outlawing street protests, jailing dissidents and intensifying prosecutions under a draconian royal defamation law.

In response to the coup, the US trimmed back military aid and distanced itself from the regime.

But relations are on a better footing under Trump, with US Secretary State Rex Tillerson in August becoming the highest-level US official to stop in the kingdom since the 2014 coup. He was warmly received by a beaming Prayut.  

The thaw comes amid Washington's concerns of rival superpower China's growing clout in the region.

Beijing woos its smaller neighbours with massive investment packages free of pressure to safeguard human rights or democratic principles.

With US relations put on ice after the coup, Thailand's generals have cosied up to China, welcoming infrastructure investment and arms deals. 

On Tuesday Prayut tried to allay suspicions that the meeting with Trump was a realignment of alliances. 

"Please don't consider this as me taking a side," he said. "We are cooperating with all superpowers, and both large and small countries."

Prayut has promised a return to democracy but the timetable keeps slipping and there is currently no scheduled date. 

Even if a poll is eventually held, it will be organised under a new junta-drafted charter that significantly curbs the power of elected politicians and enshrines the military's oversight of any future government for the next 20 years.

The two leaders may find they have much in common when they meet next week. 

Like Trump, the straight-talking and often bellicose Prayut enjoys berating the media and speaking off the cuff at length -- including during weekly "Bringing Happiness Back to Thailand" speeches that are broadcast on all channels.