North Korea launched a ballistic missile Tuesday as the US prepared to mark its Independence Day, triggering a Twitter outburst from President Donald Trump who urged China to "end this nonsense once and for all".
Analysts said the rocket could bring Alaska within range of the North' devices.
The launch was the latest in a series of provocations that have ratcheted up tensions over the nuclear-armed North' weapons ambitions, and came days after Seoul' new leader Moon Jae-In and Trump focused on the Pyongyang threat in their first summit.
The "unidentified ballistic missile" was fired from a site in North Phyongan province, the South' Joint Chiefs of Staff said in a statement, and came down in the East Sea, the Korean name for the Sea of Japan.
It flew for "more than 930 kilometres", they added.
The device may have come down in Japan' exclusive economic zone, a spokeswoman for Tokyo' defence ministry told AFP - waters extending 200 nautical miles from its coast.
Japanese Chief Cabinet Secretary Yoshihide Suga said the missile flew "for about 40 minutes" - an unusually long flight time, with Prime Minister Shinzo Abe telling reporters: "This launch clearly shows that the threat has grown."