WASHINGTON — The United States imposed sanctions Tuesday on a Myanmar general who it says violated a U.N. Security Council ban on buying military goods from North Korea despite Myanmar's assurances it has severed such ties.

Lt. Gen. Thein Htay is the head of the Directorate of Defense Industries, which the U.S. designated for sanctions a year ago, saying that organization has carried out missile research and development, and used North Korean experts.

The latest U.S. action does not target Myanmar's reformist government, which has continued to take positive steps in severing military ties with the North, the Treasury said. That's been a key goal of the Obama administration's engagement with the government of President Thein Sein, who has introduced democratic changes after decades of authoritarian rule that had led to international isolation.

Washington says the arms trade provides Pyongyang with revenue for its nuclear and missile programs that threatens the U.S. and its allies. North Korea has conducted long-range rocket and atomic tests in the past year that have deepened concerns about its weapons' capabilities.

In response to Myanmar's reforms, the U.S. has eased its longstanding restrictions on trade and investment in the impoverished Southeast Asian country but it still enforces targeted sanctions against individuals it considers to be bad actors.

"Thein Htay has disregarded international requirements to stop purchasing military goods from North Korea, the revenues from which directly support North Korea's illicit activities," said David S. Cohen, undersecretary for terrorism and financial intelligence. His statement did not specify the goods that were purchased.

Thein Htay took part in a secret visit by top Myanmar military officials to North Korea in late 2008. They visited military facilities, and according to the State Department, signed a memorandum of understanding with North Korea to provide assistance to Myanmar to build medium range, liquid-fueled ballistic missiles.

It's unclear what kind of military hardware and know-how Myanmar has actually obtained from North Korea. The leader of the 2008 mission, then-junta No. 3, Shwe Mann, has since renounced the military trade with the North. Tuesday's action, however, reflects U.S. concerns that Thein Htay has allowed it continue.

Shwe Mann, who is now speaker of the lower house of parliament and is considered an advocate of democratic reform, was taken off the U.S. sanctions list last September. As chief of Myanmar's ruling party, he has cooperated with opposition leader and Nobel laureate Aung San Suu Kyi.

Shwe Mann told The Associated Press during a visit to Washington last month that Myanmar's arms trade with North Korea has stopped.

"If there's any information that we hear on this matter we will continue to take actions as required. Because our country, like others, will abide by the resolutions of the United Nations Security Council," he said. "We are not neglecting this matter."