WASHINGTON — The U.S. and South Korea have called on China to use its influence over Russia and North Korea to prevent escalation after Pyongyang sent thousands of troops to Russia to aid Moscow's war against Ukraine . Beijing has so far stayed quiet. In a rare meeting earlier this week, three top U.S. diplomats met with China’s ambassador to the United States to emphasize U.S. concerns and urge China to use its sway with North Korea to try to curtail the cooperation, according to a State