Thailand has said it was halting progress on a peace agreement with Cambodia, signed last month in Malaysia and overseen by US President Donald Trump, after a landmine explosion at the border injured several Thai soldiers on Monday.

Thailand and Cambodia fought a five-day border conflict in July that killed dozens of people and displaced about 200,000 on both sides of the border.

An initial ceasefire between the two Southeast Asian countries was agreed on July 28 after the US president held calls with the respective leaders. Thailand and Cambodia then signed a peace declaration in Malaysia in late October in a ceremony witnessed by Trump and Malaysian Prime Minister Anwar Ibrahim.

On Monday, the supreme commander of Thailand’s armed forces, Gen. Ukris Boontanondha, said he was “halting all agreements until Cambodia clearly and sincerely demonstrates that it will not be ‘hostile’,” according to a Facebook post from Thailand’s armed forces.

Thailand’s Prime Minister Anutin Charnvirakul said: “Everything must stop.”

“What we have been implementing all along — at this point, must now be considered halted until there is clarity,” Anutin said at the Royal Thai Police headquarters Monday.

“What has happened has meant that the hostility that we thought would decrease against the threat to national security has not decreased. Since it has not decreased, we cannot proceed with anything beyond this.”

The apparent major U-turn came after a landmine explosion injured four Thai soldiers in Sisaket province, northeastern Thailand, on the volatile border with Cambodia Monday.

One soldier’s right leg was severed in the blast, while another suffered shrapnel wounds to the leg, the army said. The incident happened while troops were on a “routine patrol along a frequently used route,” said Maj. Gen. Winthai Suvaree, spokesperson for the Royal Thai Army.

Thailand accused Cambodia of laying fresh landmines following the removal of a barbed wire fence, which was discovered on November 9.

Winthai said the discovery “violates the signed joint declaration and will inevitably impact Thailand’s stance and various agreements.”

CNN cannot independently verify the claims that Cambodian troops laid fresh landmines.

The Cambodian government said in a statement it “categorically denies the allegations,” adding that it has not deployed new landmines “and will never do so.”

Cambodia also said it is “gravely concerned” about reports that Thailand has suspended the peace declaration and it remains committed to implementing the peace accord.

“Most minefields, from nearly three decades of Cambodia’s civil wars of the 1970s and 1980s, along the Cambodia-Thailand border have not yet been cleared due to the difficult terrains and the un-demarcated status of the border areas,” Cambodia’s Ministry of Foreign Affairs said in the statement.

“The situation remains calm,” Cambodia’s Ministry of Defense spokesperson said Tuesday after military forces from both sides communicated following the landmine explosion.

The announcement from Thailand also calls into question the already tentative release of 18 Cambodian prisoners of war, who were scheduled to be handed over under the terms of the declaration.

A fragile peace agreement

In late October, Trump traveled to Malaysia as part of his three-leg tour of Asia and presided over the signing of a peace declaration between the leaders of Thailand Cambodia amid lavish praise of the US president for his mediation efforts in the border conflict.

The moment was considered by Trump as a major diplomatic victory, and another fillip to his much vaunted – and often over-exaggerated – campaign to have ended several wars.

Thailand and Cambodia have fought brief skirmishes in recent decades over their disputed border and the fighting earlier was some of the most serious in years. Each side accused the other of starting the latest border flare-up and traded blame for the clashes.

Trump had warned the two leaders that he would not make trade deals with either if the conflict continued – a threat that came as both faced elevated tariffs from the US under Trump’s global trade war.

The peace declaration included a commitment to withdraw heavy weapons from the border, de-mining efforts, and to de-escalate tensions that erupted into the brief but deadly border conflict.

The agreement was built on the truce signed in July, but fell short of a “peace treaty,” despite Trump repeatedly describing it as such. And analysts had cautioned of a long road ahead before a lasting peace deal would be achieved.

Anutin had qualified the signing ceremony as a “concrete step towards peace” that would hinge on “full implementation” of the declaration. And Thai diplomats were carefully reticent about the joint declaration, calling it a “reaffirmation” of a ceasefire both sides agreed to in July.

Hun Manet, the prime minister of Cambodia announced at the time “a strong commitment to fully and faithfully implementing this joint declaration.”

The issue of landmines along the Thai-Cambodia border has also been a major point of contention for the Thais. The most recent border flare-up came after five Thai soldiers were injured in a landmine explosion, with the incident prompting Thailand to downgrade diplomatic relations with its neighbor.

In recent decades, Thailand and Cambodia have had a complicated relationship of both cooperation and rivalry. The two countries share a 500-mile (800-kilometer) land border – largely mapped by the French when they controlled Cambodia as a colony – that has periodically seen military clashes.

Cambodia has previously sought a ruling from the UN’s International Court of Justice over disputed areas. However, Thailand does not recognize the ICJ’s jurisdiction and claims that some areas along the border were never fully demarcated, including the sites of several ancient temples.

The site of the most recent landmine explosion was in an area close to Cambodia’s Preah Vihear temple, a UNESCO World Heritage site that has been at the center of previous military clashes.

The peace declaration did not resolve the territorial dispute over the two countries’ shared border. (CNN)