U.S. to keep up economic pressure on North Korea after nuclear blast

NEW YORK (Reuters) - The United States will do all it can to oppose North Korea's nuclear weapons policy by using financial tools since coordinated economic sactions have shown to work, U.S. Treasury Secretary Jack Lew said on Monday. "I think sanctions have effectively cut North Korea off from the global economy," Lew said three days after Pyongyang set off its most powerful nuclear blast to date and said it had mastered the ability to mount a warhead on a ballistic missile. "North Korea is an enormous challenge and we will do everything we can to keep the pressure on them. We will continue to sharpen financial tools as we can. The goal is to change the (North Korean nuclear weapons) policy," he said, adding China's participation is very important. "We've seen no sign of a change in policy," he said, adding the United States is not about to relax sanctions. (Reporting by Jonathan Spicer; Editing by Chizu Nomiyama)