Myanmar's embattled junta has banned anyone eligible for military conscription from leaving the country without permission, as it seeks to shore up its forces fighting rebel groups opposed to its rule.

The junta has lost control of swathes of the country to ethnic minority armed groups and other opposition forces in the civil war triggered by its coup d'etat four years ago.

A long-dormant conscription law was enforced last year as the army reeled from a string of battlefield defeats to ethnic armed groups and civilian "People's Defence Forces" seeking to oust it from power.