Suspected North Korean hackers have already targeted the exercises, with email attacks on South Korean contractors working at the allies’ combined exercise war simulation centre, police have said.
The announcement of the cruise missile test also comes days after US President Joe Biden hosted South Korean leader Yoon Suk-yeol – along with Japanese Prime Minister Fumio Kishida – at Camp David.
At a press conference on Friday the leaders said they saw a “new chapter” of close three-way security cooperation after the summit, which would have been unthinkable until recently due to the legacy of Japan’s harsh 1910 to 1945 occupation of the Korean peninsula.
It was the first time the three countries’ leaders have met for a standalone summit, and while China was the main topic, they also discussed North Korea.
The three leaders agreed to a multi-year plan of regular exercises in all domains, going beyond one-off drills in response to Pyongyang, and made a formal “commitment to consult” during crises, with Biden saying they would open a hotline.
The leaders also agreed to share real-time data on North Korea and to hold summits every year.