By David Brunnstrom and Steve Holland WASHINGTON (Reuters) – The United States is concerned North Korea’s escalating missile tests could be precursors to resumed tests of nuclear weapons and intercontinental ballistic missiles, a senior U.S. official said on Sunday, while urging Pyongyang to join direct talks with no preconditions. North Korea conducted its largest missile test since 2017 on Sunday, sending a suspected intermediate-range ballistic missile soaring into space. South Korean President Moon Jae-in said a recent flurry of North Korean missile tests was reminiscent of heightened tens…