The escalation follows a smaller exchange of fire on Sunday. Thailand said Cambodian forces wounded two of its soldiers before Thai troops responded for roughly 20 minutes. Cambodia claimed Thailand initiated that encounter as well and said it did not return fire.
Tensions have persisted despite an October ceasefire negotiated by U.S. President Donald Trump, which brought an end to five days of fighting in July that killed dozens of soldiers and civilians. That agreement showed signs of strain last month when several Thai soldiers were injured by land mines in contested areas, leading the Thai government to announce it would suspend implementation of parts of the deal.
Both sides have continued to blame one another for ceasefire violations, even as the truce calls for cooperation on mine removal and steps to stabilize the border.
Thailand and Cambodia have a long history of conflict dating back to rival kingdoms that fought over influence for centuries. In the modern era, disputes have centered on French colonial-era border maps, which Thailand argues are inaccurate.
Despite the October agreement, neither country has reached a resolution to the underlying territorial dispute, and regional observers warn that renewed clashes could draw the two nations closer to a wider conflict without renewed diplomatic engagement.