The U.N. High Commissioner for Refugees estimates that more than 450,000 refugees and internally displaced people can't return home because of land mines in northern and southeastern states.
"There will be no active promotion of return until land mines areas are identified, openly marked and cleared," UNHCR protection office Maja Lazic said.
The United Nations said 14 years of conflict between the military and as many as 17 armed groups has left Myanmar strewn with anti-personnel mines.
Myanmar is trying to erase the legacy of the military-led government. Reforms that started with general elections in 2010 were welcomed, though recent conflict between Buddhists and Muslims has overshadowed reforms.
The United Nations says mine clearance can't take place in Myanmar until national security is ensured. Mine awareness groups say it may take years before the extent of mine contamination is known.
"The process requires agreement, cooperation and support from conflict parties," Lazic said.