HONG KONG (AP) — A Treasury official says she urged officials in Hong Kong and Beijing to step up measures to counter North Korean smuggling and financing, as the U.S. fine tunes efforts to shut down Pyongyang's nuclear program.

Treasury Undersecretary for terrorism and financial intelligence Sigal Mandelker said Wednesday that she told Hong Kong officials it should be harder for North Korea to use shell companies registered in the Asian business hub.

Mandelker said she "pressed repeatedly" to officials in Beijing that they should expel sanctioned people who facilitate North Korean financial transactions.

She said three increasingly stringent U.N. Security Council resolutions last year on North Korea were having a "significant impact" but did not give any details.