Victims were patients and employees under 30, an anti-junta group said.
New data shows the military killed nearly 90 people in the region in the first quarter of 2024.
Eight more were injured after police, guards and soldiers opened fire on the inmates, an advocacy organization said.
The Mon State Revolutionary Force and Mon State Defense Force were formed after the 2021 coup.
Those who refuse to denounce the Arakan Army are made to pay fines.
Fighting between the Arakan Army and the Arakan Resistance Solidarity Army has caused 3,000 to flee.
Airstrikes and artillery killed nearly 400 civilians in the first quarter of 2024, RFA data shows.
The Myanmar army is experiencing a rapid rise in defections and military losses, posing questions about the continued viability of the junta’s grip on power.
More than 30 weapons were seized from the junta’s base camp, an official said.
Khalil Al-Hayya did not say whether his apparent embrace of a two-state solution would amount to an end to the Palestinian conflict with Israel or an interim step toward the group's stated goal of destroying Israel.
Peace requires turning against the junta, not trying to prop up its dying power through negotiations.
Myanmar community members applied to the courts to bar the diplomat from attending the Association of Southeast Asian Nations.