The Biden administration confirmed Thursday that North Korea recently conducted two tests of a relatively new intercontinental ballistic missile system, ratcheting up tensions between leader Kim Jong Un and the U.S. at a precarious time in world politics. A senior administration official, who spoke on the condition of anonymity in order to share details of the government’s threat assessment, said the tests were carried out in February and March. North Korea conducted its last ICBM test in November 2017. World leaders first learned of this particular ICBM system, which can carry nuclear weapons, during North Korea’s Workers’ Party parade, which...