North Korea has announced that it plans to launch a satellite as soon as Monday, according to Japanese authorities the same day, potentially coinciding with a trilateral summit between South Korea, Japan and China.

Pyongyang notified Tokyo of plans to conduct the launch of what would likely be a military spy satellite between May 27 and June 4, according to the Japanese Prime Minister’s Office in an overnight statement. The office added that Japan should be prepared for “unforeseen circumstances.”