A senior U.S. diplomat left Myanmar on Friday still concerned about the government's human rights policies and its relations with North Korea, despite a recent change of leadership.

Joseph Yun's visit was the first by a senior American official since a nominally civilian government took over from the ruling junta in late March and was meant to investigate the prospects for reform. Washington is carefully watching the new leaders because President Barack Obama has pinned his new policy on Myanmar on hopes that dialogue — in contrast to the previous isolation — will persuade the repressive regime to change.

Yun, the deputy assistant secretary of state for East Asian and Pacific Affairs, concluded the three-day visit after meeting with officials, ethnic minority representatives and pro-democracy leader Aung San Suu Kyi, an embassy statement said.

In his meetings with officials, Yun reiterated the United States' willingness to improve relations but said it would depend on the government's "taking meaningful, concrete steps toward democratic governance, respect for human rights and the release of all political prisoners," the statement said.

Yun also expressed concerns about Myanmar's military relationship with North Korea and called on it to abide U.N. resolutions.

A U.N. Security Council resolution bans all North Korean arms exports, authorizes member states to inspect North Korean sea, air and land cargo, and requires them to seize and destroy any goods transported in violation of the sanctions.

Arms experts says Myanmar — which faces an arms embargo from many Western states — gets weaponry from Pyongyang. Some analysts have suggested North Korea shares missile and nuclear technology with Myanmar, though the evidence is thin.

While the statement offered no upbeat assessments about the government, it did say that Yun and Suu Kyi "had a useful conversation about how best to promote inclusive dialogue and national reconciliation to fulfill the needs and desires of all Burmese."

Washington, like pro-democracy advocates, prefers to use the old name "Burma" for the Southeast Asian country.

Yun last visited Myanmar in December.

Relations between Myanmar and the U.S. have been strained since its military crushed pro-democracy protests in 1988, and Washington has been Myanmar's strongest critic, applying political and economic sanctions against the junta.

But the Obama administration has switched to a policy of engagement in hopes of coaxing democratic change. Washington still insists that the government release political prisoners, estimated at more than 2,000 by the U.N. and human rights agencies.

The government on Monday released more than 14,000 prisoners, including about 55 political ones, from jails across the country under a clemency program. But the limited nature of the program has drawn criticism from many who had expected more generous terms.