Cambodian and Thai troops exchanged fire in a new round of clashes at a disputed border area on Thursday, both sides said.

Both the Cambodian Defense Ministry and the Thai army accused the other side of firing first in the incident, the latest flare-up in a long-running row over border demarcation near two ancient temples.

The incident came as the two neighbors downgraded their diplomatic ties.

What does Cambodia say?

A spokesperson for Cambodia's Defense Ministry said there had been an unprovoked incursion by Thai troops, and Cambodian forces had responded in self-defense.

Cambodia's former Prime Minister Samdech Techo Hun Sen said that two Cambodian provinces had come under shelling from Thailand's military.

In a post on his Facebook page, Hun Sen called for calm and urged Cambodians to place their trust in the Cambodian armed forces and government.

What does Thailand say?

In a statement, the Thai military said Cambodian troops had opened fire in an area near the disputed Ta Moan Thom temple. It said Cambodia had deployed a surveillance drone before sending troops to the area with heavy weapons.

The situation at Thailand's border with Cambodia remains delicate and must be addressed with care and with measures in line with international law, Thailand's acting Prime Minister Phumtham Wechayachai said on Thursday.

Ties to be downgraded 

The clash came after Thailand recalled its ambassador to Cambodia on Wednesday and said it would expel Cambodia's envoy in Bangkok, after a second Thai soldier in the space of a week lost a limb to a landmine in the disputed area.

In response, Cambodia has downgraded diplomatic ties with Thailand to the lowest level and recalled all of its diplomatic staff from Bangkok, the Cambodian Foreign Ministry's spokesperson Chum Sounry said early on Thursday.

Thailand has said the landmines had been placed in the area recently, which Cambodia has described as a baseless allegation.

(With input from agencies)