Burma freed at least 200 political prisoners on Friday in an amnesty that could embolden the opposition and put pressure on the West to lift sanctions as one of the world's most reclusive states opens up after half a century of authoritarian rule.

Among those freed are long-persecuted democrats and powerful ethnic leaders whose proven ability to organise and inspire others could heap pressure on president Thein Sein to accelerate his nascent reforms.

The United States and Europe have said freeing political prisoners is crucial to even considering lifting the economic sanctions that have isolated the former British colony and pushed it closer to China during five decades of often-brutal military rule that ended last March.