Thailand has imposed restrictions on all travellers heading into Cambodia, as the two countries remain locked in a bitter border dispute.

The ban applies to any vehicle or person trying to cross into Cambodia from checkpoints across several Thai provinces, as well as foreign tourists flying into Siem Reap.

The military said in a statement on Monday that the new restrictions "matched the current security situation".

Bilateral relations between the two countries are at their worst in more than a decade, after armed clashes along the border in May left one Cambodian soldier dead.

Since then, the two countries have imposed punitive measures on each other. Cambodia has banned imports from Thailand, ranging from fruit and vegetables to electricity and internet, as well as Thai dramas and films.

Exemptions to the latest travel ban may be granted on humanitarian grounds - such as for students or medical patients - at the discretion of officials at the checkpoints, Thai authorities said.

The restrictions would also help to counter illegal scam operations in Cambodia, according to the military.

On Monday, Thai Prime Minister Paetongtarn Shinawatra vowed to crack down on scam operations in Cambodia, with measures including suspending internet services used by Cambodian security agencies.

She added that foreign tourists would also be banned from taking flights from Thailand to the popular Cambodian resort town of Siem Reap.

Thailand previously implemented similar measures on neighbouring Myanmar, which is also home to thriving scam networks that have entrapped thousands of foreigners.

The dispute between Thailand and Cambodia has plunged Paetongtarn Shinawatra's government into the throes of a political crisis, after a leaked phone call between her and Cambodia's strongman ex-leader Hun Sen.

In the phone call, Paetongtarn was heard calling him "uncle" and telling him to ignore a Thai military commander who "just wanted to look cool".

Paetongtarn defended her demeanour as a "negotiation technique", but critics said she undermined Thailand's politically influential army. A key coalition partner of her Pheu Thai party has since left the alliance.

Tensions between the two countries date back more than a century, when the borders were drawn after the French occupation of Cambodia.