Thailand has launched air strikes along its disputed border with Cambodia, the Thai military said on Monday, after both countries accused the other of breaching a ceasefire agreement brokered by US President Donald Trump.

At least one Thai soldier has been killed and four wounded in the fresh clashes that broke out around two areas in the easternmost province of Ubon Ratchathani, Thailand's military said in a statement, after its troops came under Cambodian fire.

"The Thai side has now begun using aircraft to strike military targets in several areas," the statement said.

Cambodia's defence ministry said in a statement that the Thai military had launched dawn attacks on its forces at two locations, following days of provocative actions, and added that Cambodian troops had not retaliated.

Former Cambodian prime minister Hun Sen, the father of the current leader, urged his country's forces to exercise restraint, saying Thai "aggressors were trying to draw us into retaliating" and that the "red line for responding had already been set".

The border dispute had erupted into a five-day war in July, before a ceasefire deal brokered by Malaysian Prime Minister Anwar Ibrahim and Trump, who also witnessed the signing of an expanded peace agreement between the two countries in Kuala Lumpur in October.

At least 48 people were killed and an estimated 300,000 temporarily displaced during the July clashes, with the neighbours exchanging rockets and heavy artillery fire.

But following a landmine blast last month that maimed one of its soldiers, Thailand said it was halting the implementation of the ceasefire pact with Cambodia.

In Thailand, more than 385,000 civilians across four border districts are being evacuated, with over 35,000 already housed in temporary shelters, the Thai military said.

Thailand and Cambodia have for more than a century contested sovereignty at undemarcated points along their 817-km land border, first mapped in 1907 by France when it ruled Cambodia as a colony.

Simmering tension has occasionally exploded into skirmishes, such as a weeklong artillery exchange in 2011, despite attempts to peacefully resolve overlapping claims. (Reuters)