A small drone landed on the Tokyo office of Japanese Prime Minister Shinzo Abe Wednesday, then later tested positive for radiation.
The drone measured about 20 inches in diameter and was carrying a flare bearing the symbol for radioactivity, a water bottle, and a camera, Reuters reported.
An official found the drone, which did not cause injuries or damage.
Authorities later tested the drone and found low levels of radiation, according to Kyodo.
The source of the radiation, as well as the origin and objective of the drone, remained a mystery Wednesday. However, Reuters did point out that the incident took place the same day that a court allowed a nuclear power plant to restart operations.
Abe was in attending a summit in Indonesia when the drone was discovered.