The leaders of Thailand and Cambodia were set to hold talks in Malaysia on Monday to reach a ceasefire in their deadly border dispute, with the United States saying its officials would be assisting in the peace process.

Cambodian Defense Ministry spokesperson Lt. Gen. Maly Socheata accused Thai forces of escalating the violence with bombardment of Cambodian territory early Sunday, followed by a “large-scale incursion” involving tanks and ground troops in multiple areas.

Thailand and Cambodia have agreed to hold talks in Malaysia on Monday in an attempt to negotiate an end to a conflict that has lasted four days.