Thailand and Cambodia agreed to an "immediate" ceasefire on Dec. 27, the two countries said in a joint statement, pledging to end border clashes that killed dozens of people.
U.N. Secretary-General Antonio Guterres welcomed the announcement "as a positive step towards alleviating the suffering of civilians... and creating an environment conducive to achieving lasting peace," spokesman Stephane Dujarric said.
At least 47 people were killed and more than 1 million displaced in three weeks of fighting with artillery, tanks, drones and jets, according to official tallies.
The conflict spread to nearly every border province on both sides, shattering an earlier truce for which U.S. President Donald Trump took credit.
U.S. Secretary of State Marco Rubio on Saturday welcomed the ceasefire, calling on both sides to "immediately honor this commitment."
The ceasefire took effect at 12 p.m. local time, said the declaration signed by the Southeast Asian neighbors’ defense ministers at a border checkpoint on the Thai side.
The truce applies to "all types of weapons, including attacks on civilians, civilian objects and infrastructures, and military objectives of either side, in all cases and all areas."
Both sides agreed to freeze all troop movements and allow civilians living in border areas to return home as soon as possible, the statement said.
They also agreed to cooperate on demining efforts and combatting cybercrime, while Thailand was to return 18 captured Cambodian soldiers within 72 hours.
Thai Defense Minister Nattaphon Narkphanit said the initial three-day window would be an "observation period to confirm that the ceasefire is real."
