A new US envoy to Burma ended his first visit to the country on Wednesday by urging “genuine and concrete” reforms by the army-backed regime and said Washington would respond “in kind”.

Derek Mitchell, who was appointed as the first US coordinator for policy on Burma last month, said the Southeast Asian nation should begin by releasing political prisoners, ending ethnic conflicts and reaching out to critics.

Mitchell urged Burma to “prove the sceptics wrong” as he prepared to leave the country after a visit that included talks with ministers of the new nominally-civilian government and opposition icon Aung San Suu Kyi.

“I noted that progress on these issues will be essential to progress in the bilateral relationship, and that if the government takes genuine and concrete action, the United States will respond in kind,” he told reporters at Rangoon airport.

Mitchell, who was on his first official visit to the country as part of Washington’s strategy of engagement, did not directly mention the wide ranging sanctions imposed against Burma by the US.

But he said he had discussed American “policy approaches” with Suu Kyi and her party.

Mitchell called for the release of the approximately 2,000 political detainees and voiced fears over “serious human rights violations, including against women and children” linked to hostilities in ethnic minority areas.

The envoy also said the US was concerned about the “lack of transparency” in Burma’s military dealings with North Korea.

US diplomatic memos released last year by WikiLeaks said Washington has suspected for years that Burma ran a secret nuclear program supported by Pyongyang.

In May, a US Navy destroyer intercepted a North Korean cargo ship in the South China Sea suspected of carrying missiles or other weapons, that may have been destined for Burma, and made it turn back.

Mitchell’s post was created in 2008 when US Congress, under then-president George W. Bush, approved a law that tightened sanctions against Burma, but the position was not filled at the time due to a political dispute.

After taking power in 2009, President Barack Obama’s administration changed tack, concluding that the measures aimed at isolating Burma had been ineffective.

Burma’s government has recently appeared to be seeking to improve its image by reaching out to critics such as Suu Kyi, who last month met President Thein Sein, a former general, for the first time.

The Nobel peace prize winner was released from seven straight years of house arrest by the junta days after controversial November elections.