US Secretary of State Hillary Clinton said that Myanmar needed to do "much more" to improve human rights despite what she saw as signs of change by the military-backed government.
Clinton, in Hawaii for an Asia-Pacific summit, reiterated that she believed there were "real changes" under way as the United States pursues an engagement policy with the country formerly known as Burma.
"But we know there must be much more done. We are concerned about the human rights situation," Clinton told a news conference on Friday.
"We continue to call for the unconditional release of all political prisoners and an end to the violence in ethnic minority areas," she said.
Clinton also urged Myanmar to be more transparent in its relationship with North Korea after allegations that the two nations, long pariahs to the West, have collaborated in areas including nuclear technology.
"We believe that the Burmese people share the same universal values that all people are entitled to and therefore we want to see the encouraging signs continue and strengthen," she said.
Clinton voiced hope that such changes would lead to "a transition to a broader political dialogue and eventually the kind of democratic and open society that we think would benefit the people of Burma."
Myanmar's generals last year freed democracy icon Aung San Suu Kyi and later nominally handed over control to civilians. The new government has surprised observers with populist measures such as freeing 200 political prisoners and defying China by freezing work on an unpopular dam.
Critics say that the changes are cosmetic and argue that Myanmar has at best reverted to its situation before a bloody crackdown on protests led by Buddhist monks in 2007.