Thailand and Cambodia agreed on Saturday to halt weeks of fierce border clashes, the worst fighting in years between the Southeast Asian countries that has included fighter jets sorties, exchange of rocket fire and artillery barrages.

"Both sides agree to maintain current troop deployments without further movement," their defence ministers said in a joint statement on the ceasefire, to take effect at noon (0500 GMT).

"Any reinforcement would heighten tensions and negatively affect long-term efforts to resolve the situation," according to the statement released on social media by Cambodia's Defence Ministry.

The agreement, signed by Thai Defence Minister Natthaphon Nakrphanit and his Cambodian counterpart Tea Seiha, ended 20 days of fighting that has killed at least 101 people and displaced more than half a million on both sides.

The clashes were re-ignited in early December after a breakdown in a ceasefire that US President Donald Trump and Malaysian Prime Minister Anwar Ibrahim had helped broker to halt a previous round of fighting.

For more than a century, Thailand and Cambodia have contested sovereignty at various undemarcated points along their 817km (508 miles) land border - a dispute that has occasionally exploded into skirmishes and fighting.

The latest ceasefire would be monitored by an observer team from the Association of Southeast Asian Nations (ASEAN) regional bloc as well as direct coordination between both countries, Natthaphon said.

"At the same time, at the policy level, there will be direct communication between the minister of defence and chief of the armed forces of both sides," he told reporters.

Trump intervention

Simmering tensions between the two countries came to a head in July this year, when the neighbours clashed for five days along some parts of the frontier, leaving at least 48 people dead and 300,000 displaced before Trump intervened to bring about a truce.

That ceasefire broke down in early December with the two sides accusing each other of moves that led to clashes.

Since the conflict restarted, neither Anwar - currently ASEAN chair - nor Trump were successful in stitching together another ceasefire, as fighting spread from forested regions near Laos to the coastal provinces on the Gulf of Thailand.

The renewed parleys came after a special meeting on Monday of Southeast Asian foreign ministers in Kuala Lumpur, followed by three days of talks between the warring sides at a border checkpoint, where the two defence ministers met on Saturday.

In their joint statement, the ministers agreed on the return of people displaced from affected border areas, while also underlining that neither side would use any force against civilians.

Thailand will also return 18 Cambodian soldiers in its custody since the July clashes if the ceasefire is fully maintained for 72 hours, according to the agreement.

Saturday's pact, however, made clear that it will not impact any border demarcation activities underway between both countries, leaving the task of resolving disputed areas along the frontier to existing bilateral mechanisms.

"War and clashes don't make the two countries or the two people happy," Thailand's Air Chief Marshal Prapas Sornjaidee told reporters. "I want to stress that the Thai people and the Cambodian people are not in conflict with each other."