The United States Congress will push to tighten the screw on North Korea with legislation making the communist nation's access to the global financial system more difficult, diplomatic and congressional sources said Sunday.

Rep. Ed Royce (R-CA), the chairman of the U.S. House Committee on Foreign Relations, is working on a bill aimed at tackling Pyongyang's ability to gain hard currency, according to the sources.

The move is part of a series of reactions by the U.S. Congress to North Korea's nuclear test last week, while the Obama administration is focusing on first hammering out a unified response by the U.N. Security Council.

"Rep. Royce is expected to submit a related bill in a few weeks," a source said. "I think now calls for far-reaching measures designed to cut North Korea's financial ties with the outside world."

In an interview with Yonhap News Agency in December before Pyongyang's rocket launch, Royce said, "I think it is the time to respond with an asset freeze as we did before with Banco Delta Asia (BDA)."

He was referring to a 2005 freeze of US$24 million in North Korea's assets at the Macau-based BDA by the Treasury Department, a measure intended to squeeze North Korea's financial sources for nuclear and missile programs.

The financial measure sent a clear message to other financial institutions with ties with Pyongyang and it was apparently more painful for the isolated nation than any other ones like an arms embargo and restrictions on trade and travel.

It remains uncertain whether such a BDA-style strategy will sting North Korea again amid widespread speculation that it has already taken measures to avoid impacts.

As to a question about whether the U.S. has more cards to play against North Korea, already subject to a range of sanctions, State Department Spokeswoman Victoria Nuland said last week, "We still do have some leeway. I would say that we continue to review what will be most effective." She did not elaborate. (Yonhap News)