WASHINGTON (AP) — The United States imposed sanctions Tuesday on a Myanmar military officer and three companies it accuses of involvement in the continuing, illicit arms trade with North Korea.

The designations do not directly target Myanmar's government but will deepen doubts over the nation's compliance with U.N. Security Council resolutions.

Cutting Myanmar's military ties with North Korea has been a key goal of the U.S. policy to end Myanmar's long international isolation after its democratic reforms.

In response to the reforms in the country also known as Burma, Washington has eased its longstanding restrictions on trade and investment, although not on export of arms. In a sign of enduring U.S. concerns, Treasury has periodically expanded the blacklist of individuals and companies it considers to be bad actors.

As of Tuesday, they include Lt. Col. Kyaw Nyunt Oo, said to act on behalf of the Burmese Directorate of Defense Industries, or DDI, which is already sanctioned. Its chief, a general, was blacklisted in July.

Treasury also targeted Soe Min Htike Co. Ltd. and Excellence Mineral, describing them in Tuesday's statement as Myanmar companies working with North Korean officials to import materiel for military weapons programs as recently this June; and Asia Metal, said to have constructed buildings and supplied construction materials for a DDI factory compound where approximately 30 North Koreans were still working as of December 2012.

Myanmar's government has said its arms trade with North Korea has stopped and it complies with the U.N. sanctions which are intended to deny Pyongyang revenue for expanding nuclear and ballistic missile programs. U.S. officials say Myanmar has curtailed the trade, but not ended it.

"The revenues from these continuing military sales directly support North Korea's illicit activities," Under Secretary for Terrorism and Financial Intelligence David S. Cohen said in a statement. "We will continue to target this activity in Burma, and the region, as we work with our international partners to shut down North Korea's dangerous and destabilizing weapons proliferation."

Designation of a company or individual on the Treasury list prohibits U.S. persons from transactions with them, and freezes any assets they may have subject to U.S. jurisdiction.

The military cooperation with North Korea was forged during Myanmar's international isolation. The State Department has said that in late 2008, when Myanmar officers visited Pyongyang, they signed a memorandum of understanding with North Korea on assistance to build medium range, liquid-fueled ballistic missiles.