Cambodia and Thailand on Sunday signed an expansion of a ceasefire that U.S. President Donald Trump helped broker over the summer to end their border conflict.

Trump threatened higher tariffs against both countries to push them into agreeing to end the fighting. Dozens of people were killed and hundreds of thousands were displaced in the conflict.

The president watched as Cambodian Prime Minister Hun Manet and Thai Prime Minister Anutin Charnvirakul signed the expanded ceasefire at the annual summit of the Association of Southeast Asian Nations.

The agreement requires Thailand to release 18 Cambodian soldiers held prisoner and for both countries to begin removing heavy weapons from the border.

The Associated Press contributed to this report.