Hun Sen stated his intention to restart the "important" mission in a letter published on government mouthpiece Fresh News Saturday and also shared on his official Facebook page.

It was addressed to two US state lawmakers who visited Cambodia ahead of the vote earlier this year and who this month had written to Hun Sen about reactivating the project.

The searches, which have recovered the remains of 42 American servicemen in Cambodia -- dozens are still unaccounted for -- were suspended in September 2017 as relations soured between the two countries.

Hun Sen halted it after Washington stopped issuing visas to senior Cambodian officials in reprisal for the country temporarily refusing to take in Cambodian nationals deported from the US for committing crimes.

He had also accused the US of assisting an opposition leader who was charged with treason, claims the ambassador at the time called absurd.

The rise in tensions came during the lead-up to a flawed vote in July that was swept by Hun Sen's party after the Supreme Court dissolved the main opposition.

But after securing victory, the 66-year-old strongman requested pardons for activists and opposition members who had been arrested in a crackdown on dissent before the ballot.

Analysts say Hun Sen is trying to ward off possible consequences such as potential trade sanctions by the European Union, though he has bristled at suggestions that he is under international pressure.

The programme "had been running successfully for more than 30 years, before it was suspended", Hun Sen said in his letter, adding that his government would restart cooperating with the mission with a "compassionate spirit".

America's secret bombing of Cambodia during the Vietnam War remains a sensitive subject and is a touchstone of fiery speeches by Hun Sen.

The US emerged from the Cold War as one of Cambodia's biggest donors, though the Southeast Asian country has tilted towards China in recent years thanks to loans for infrastructure and few complaints on human rights issues.