The US says a missile fired by North Korea into the Sea of Japan was an intercontinental ballistic missile.
Secretary of State Rex Tillerson called it a “new escalation of the threat” to the US and the world and warned that Washington “will never accept a nuclear-armed North Korea”.
Pyongyang earlier described it as its first successful intercontinental ballistic missile test.
US officials believe the North may now be able to fire a missile to Alaska.
However, experts say it cannot accurately hit a target.
Just hours after the North’s test, the US asked for an urgent meeting of the UN Security Council to discuss the issue. A close-door session of the 15-member body is expected on 5 July.