A U.S. specialist in Asian affairs says North Korea is making an annual profit of over two billion dollars from deals with Iran.

Larry Niksch at the U.S. Congressional Research Service claimed during a forum at the U.S. CATO Institute think tank Tuesday that in addition to financial sanctions against the North, China should block flights between Pyongyang and Tehran.

Niksch added that Washington has evidence that scientists, engineers as well as North Korea’s missiles, parts and drawings for missiles are being transferred by air between the North and Iran.