UNITED NATIONS — The United States and allies South Korea and Japan clashed with China and Russia Friday over North Korea’s latest satellite and ballistic missile launches and threats to use nuclear weapons that have escalated tensions in northeast Asia. The scene was an emergency open meeting of the U.N. Security Council called after North Korea’s failed launch of a military reconnaissance satellite on May 27 and other launches using ballistic missile technology in violation of U.N. sanctions. In response, the U.S. and its allies have carried out an increasing number of military exercises. “But two council members, China and Russia, continuously block the Security Council from speaking against the DPRK’s behavior with one voice and makes us all less safe,” he said. He warned that a planned large-scale joint military exercise on the peninsula in August “practicing a scenario involving a nuclear war” will only increase tensions.