SEOUL—North Korea test-fired a newly developed hypersonic missile this week, state news media KCNA reported on Wednesday, joining a race headed by major military powers to deploy the advanced weapons system. North Korea fired the missile off its east coast towards the sea on Tuesday, South Korea’s military said, as Pyongyang called on the United States and South Korea to scrap their “double standards” on weapons programs to restart diplomatic talks. North Korea has been steadily developing its weapons systems amid an impasse over talks aimed at dismantling its nuclear and ballistic missile arsenals in return for U.S. sanctions relief. Sung Kim, the U.S. special envoy for North Korea, said the latest launch was “destabilizing” and posed a regional threat, but Washington would continue diplomatic efforts to denuclearise the Korean peninsula. “We are waiting to hear back from Pyongyang. We have made a number of approaches … and proposed dialogues …