NEW YORK (AP) — President Donald Trump added economic action to his fiery military threats against North Korea on Thursday, authorizing stiffer new sanctions in response to the Koreans’ nuclear weapons advances. He said China was imposing major banking sanctions, too, but there was no immediate confirmation from the North’s most important trading partner.

Trump praised China for instructing its banks to cut off business with Pyongyang, but neither the Chinese nor Trump officials were ready to say so. Treasury Secretary Steve Mnuchin said he had spoken at length Thursday with the head of China’s central bank but “I am not going to comment on confidential discussions.”

If enforced, the Chinese action Trump described could severely impede the isolated North’s ability to raise money for its missile and nuclear development. China, responsible for about 90 percent of North Korea’s trade, serves as the country’s conduit to the international banking system.

Trump’s announcement of U.S. action came as he met on the sidelines of the U.N. General Assembly with leaders from South Korea and Japan, the nations most immediately imperiled by North Korea’s threats of a missile strike. His executive order adds to a U.S.-led campaign to isolate and impoverish Kim Jong Un’s government until it halts the missile and nuclear tests that, combined with Trump’s threats, have stoked global fears of war.