A Cambodian government official has sung praise to U.S. President Donald Trump for "bringing about peace" after Thailand and Cambodia agreed to a cease-fire starting at midnight local time on Monday.

After Bangkok rejected what it called the "baseless accusation" it had used chemical weapons over Cambodia during the Southeast Asian neighbours' bloodiest military clashes in decades, a months-old photo resurfaced in posts falsely claiming it showed the Thai air force using a "poisonous smoke weapon".

At least 12 have been killed in violent tensions along the disputed border separating Thailand and Cambodia. This follows a flare-up in May in which troops exchanged fire.

Thailand and Cambodia exchanged heavy artillery fire for a second day on Friday as border fighting intensified and spread, while Cambodia's leader said Thailand had agreed to a Malaysian ceasefire proposal but then backed down.