Thailand and Cambodia signed an expanded ceasefire agreement on Sunday during a ceremony attended by U.S. President Donald Trump, whose threats of economic pressure prodded the two nations to halt skirmishes along their disputed border earlier this year.

Thailand will release Cambodian prisoners and Cambodia will begin withdrawing heavy artillery as part of the first phase of the deal. Regional observers will monitor the situation to ensure fighting doesn't restart.

Cambodian Prime Minister Hun Manet called it a “historic day,” and Thai Prime Minister Anutin Charnvirakul said the agreement creates “the building blocks for a lasting peace.”

The ceremony was Trump's first event after arriving at the annual summit of the Association of Southeast Asian Nations, hosted in Kuala Lumpur.

The trip, which will continue with visits to Japan and South Korea and a potential meeting with Chinese leader Xi Jinping, is an opportunity for Trump to burnish his reputation as an international dealmaker at a time when his tariffs have scrambled the international economy and he's feuding with Democrats over a government shutdown back home.