SEOUL, Feb 19 (AFP) - North Korea said Sunday it had test-fired an intercontinental ballistic missile as a warning to Washington and Seoul, saying the successful "surprise" drill demonstrated Pyongyang's "capacity of fatal nuclear counterattack".

Leader Kim Jong Un ordered the "sudden launching drill" at 8 am Saturday (2300 GMT) and a Hwasong-15 missile -- a weapon first tested by the North in 2017 -- was fired from Pyongyang airport that afternoon, the official KCNA reported.

South Korea's military said it detected an ICBM launch at 17:22 (0822 GMT) Saturday, which Japan said flew for 66 minutes before splashing down in its Exclusive Economic Zone, with their analysis indicating it was capable of hitting the mainland United States.

North Korea's leadership hailed the test -- the country's first in seven weeks -- saying it showed "the actual war capacity of the ICBM units which are ready for mobile and mighty counterattack," KCNA said.

The launch was "actual proof" of the country's "capacity of fatal nuclear counterattack on the hostile forces", it added.

The sanctions-busting launch came just days before Seoul and Washington are due to start joint tabletop exercises aimed at improving their response in the event of a North Korean nuclear attack.

Pyongyang had last week warned of an "unprecedentedly" strong response to upcoming US-South Korea drills, which it describes as preparations for war and blames for the deteriorating security situation on the Korean peninsula.