Relations between Thailand and Cambodia suffered a major blow on Wednesday after a leak of a telephone conversation between Thai Prime Minister Paetongtarn Shinawatra and influential former Cambodian premier Hun Sen that could further escalate tensions.

Tens of thousands of people gathered in Cambodia’s capital Phnom Penh on Wednesday for a march to show their solidarity with the government and military, amid soaring tensions with neighboring Thailand following a border row that erupted last month.

The reescalation of conflict was sparked on May 28, when a Cambodian soldier was killed in an early morning clash between both nations’ troops, in an area called the Emerald Triangle—the shared border between Thailand, Cambodia, and Laos. The area remains disputed as both Thailand and Cambodia lay claims to parts of the region.