Fatal clashes have broken out between Thai and Cambodian troops along a disputed section of their border, after weeks of simmering tensions between the south-east-Asian neighbours.

At least two Thai civilians were killed and two others injured by shelling from the Cambodian side on Thursday, according to a district official, while the Thai army said that it had launched airstrikes on military targets in Cambodia.

Thailand’s military said that it had closed all border checkpoints and that fighting was taking place at six different locations.

It comes after clashes broke out near the Khmer Hindu temple, Ta Muen Thom, on Thursday morning.

Both countries accused the other of provocation.The Thai military said that Cambodian troops had opened fire near the temple, and deployed a surveillance drone before sending in troops with heavy weapons, including rocket launchers.

Cambodia denied the claims, with its ministry of national defence saying that it was the Thai military that launched the first armed assault.

The ministry said in a statement that Cambodian forces acted strictly within the “bounds of self-defence, responding to an unprovoked incursion by Thai troops that violated our territorial integrity.”

In a later statement, it condemned what it called reckless and brutal Thai military aggression, accusing its neighbour of opening fire on its troops and violating an agreement designed to de-escalate tension.

It added that Cambodia “strongly condemns the reckless and brutal military aggression of the Kingdom of Thailand against the sovereignty and territorial integrity of Cambodia,” noting that Thai fighter jets had been deployed and had dropped two bombs on a road.

Thailand said that an F-16 fighter jet had fired into Cambodia and destroyed a military target. The army said several more jets were ready to be deployed. “We have used air power against military targets as planned,” Thai Army Deputy Spokesperson, Richa Suksuwanon told reporters.

Cambodia’s influential former Premier Hun Sen – father of current Prime Minister Hun Manet – said that two Cambodian provinces had come under shelling from Thailand’s military.

In a statement posted online, Hun Manet said that Cambodia has always taken a stand to solve problems peacefully, “but in this case we have no choice but to respond with armed forces against armed aggression.”

The clashes are the latest in a history of conflict along the 817km border that Cambodia and Thailand share, sections of which are subject to overlapping territorial claims due to disagreements about colonial-era maps.

The last major clashes occurred between 2008 and 2011, when fighting and artillery exchanges killed at least 34 people, wounded many more and displaced thousands.

The hostilities between Cambodia and Thailand that have continued to escalate in recent months were initially ignited after a Cambodian soldier was killed in May in an armed confrontation in an area both countries claim as their own.

Thailand, Cambodia Downgrade Diplomatic Relations

The border tension has soured relations between the Southeast Asian neighbours, with the two sides trading barbs and tit-for-tat retaliatory measures, including the closure of border crossings.

Today’s clash came after Thailand recalled its Ambassador to Cambodia on Wednesday and said that 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.

Thailand has said the landmines had been placed in the area recently, claims that Cambodia describes as baseless.

Cambodia claims that Thai soldiers have veered off agreed jungle paths and triggered long-buried mines left behind from Cambodia’s decades of civil war.

Cambodia said that it would withdraw all of its diplomats from Thailand and ordered all Thai diplomats to leave the country.

The Cambodian government has also downgraded diplomatic relations with Thailand to the “lowest level,” reducing it to the rank of “second secretary,” according to a local news outlet.

Cambodia has also blocked imports of fuel and gas, as well as fruit and vegetables, from Thailand.