South Korean President Yoon Suk-yeol urged China to reduce the nuclear threat posed by North Korea, responding directly to Beijing’s displeasure over the U.S. ally’s new security agreement with Washington.

He also called on China to, at the very least, comply with U.N. Security Council sanctions against North Korea, according to his office late Tuesday. The statement comes days after after Beijing expressed its displeasure with the Washington Declaration signed by South Korea and the U.S. last week.

China’s compliance with the U.N. Security Council sanctions on North Korea has long been a contentious issue. As North Korea’s largest trading partner, China holds significant leverage over the isolated nation but critics say Beijing is reluctant to fully enforce sanctions fearing instability on their shared border.