The long-drawn negotiations, aimed at ending civil wars that have blighted the country for more than half a century, have snagged on whether a deal should include all rebel groups - including several still locked in combat with the army.
"This issue of all-inclusiveness is very important for the peace process," said lead government negotiator Aung Min in opening remarks, adding that the government was looking for a "practical solution".
The talks come as Myanmar's government is battling floods that have killed scores of people and left more than 330,000 affected across the country.
The quasi-civilian government, which took power four years ago, has placed the resolution of bloody ethnic conflicts at the heart of its reforms.
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In March President Thein Sein secured a draft deal with more than a dozen rebel groups to end decades of fighting, described by the United Nations as a "historic and significant achievement".
Outbreaks of sometimes heavy fighting in multiple regions have cast a shadow over the process, with lingering distrust between longstanding enemies also hampering progress.
Conflict in Kachin state has left some 100,000 people displaced since a ceasefire deal collapsed soon after the end of junta rule in 2011.
Fighting between government troops and ethnic Chinese rebels also erupted this year in the Kokang region of northern Shan state, causing tens of thousands of people to flee their homes, many into China. The Kokang rebels announced a unilateral ceasefire in June.