U.S. special envoy Derek Mitchell says Burmese officials claim they are committed to reform, but he has urged them to back up their words with concrete actions.

Mitchell, the new U.S. coordinator for Burma policy, spoke to reporters Wednesday as he was ending a five-day visit to Burma. He said he was encouraged by the openness of his conversations and the constructive tone of government officials.

But, he said, the international community remains concerned about Burma's detention of political prisoners and its treatment of ethnic minorities.

He said he told his hosts they should move quickly to demonstrate their sincerity about reform.

Mitchell was on his first visit to Burma since being confirmed to his post by the U.S. Senate last month. During the visit, he met with top government leaders in the capital, Naypyitaw. He also traveled to Rangoon to talk to Aung San Suu Kyi and other political opposition figures.

Burma's current government took office at the end of March, replacing a long-ruling military junta. Since then it has opened a dialogue with Aung San Suu Kyi, permitted visits by international human rights monitors and held so-far unsuccessful peace talks with ethnic rebels in the north, meeting key demands of the international community.

But the new government is dominated by former military officers allied with the old regime and has given no sign that it plans to release its political prisoners.