SEOUL—North Korea said Wednesday that it fired a brand-new intercontinental ballistic missile into the waters off Japan, ending a more than two-month hiatus by Pyongyang and threatening to ramp up tensions with the U.S. and in the region.

In a nationally televised broadcast, North Korea’s state television said that it had successfully fired a more advanced ICBM, which it dubbed the Hwasong-15 and which it said was capable of reaching any point on the U.S. mainland, in a launch personally ordered by leader Kim Jong Un.

Mr....