A U.S. expert on nonproliferation says UN Security Council sanctions on North Korea are working well, but the North’s expanded overseas trade is limiting effectiveness.

Senior associate at the Carnegie Endowment for International Peace, Mark Hibbs, said a Security Council report indicates the sanctions have hampered North Korea's efforts to export weapons and import items it needs to develop weapons of mass destruction.

Hibbs was referring to a report prepared by a panel of experts assessing the implementation of the UN Security Council sanctions that were slapped on the North following Pyongyang’s nuclear tests in 2006 and 2009

Hibbs said the North has seen its trade of those materials limited in part because UN member nations have upped surveillance of North Korea’s shipping fleet.

However, Hibbs said North Korea is resorting to other means to feed its "military-driven procurement programs" in response to the increased vigilance over its fleet.

He noted the North is now relying on the transshipment of goods using foreign-flagged carriers, air cargo transport, brokers operating in third countries, and the use of legitimate commerce to cover up "nefarious" transactions.