A Japanese man arrested after landing a drone with traces of radioactive material on the roof of the prime minister's office on Saturday.
Police said the unemployed man, Yasuo Yamamoto, turned himself in and admitted to flying the drone in the western city of Fukui. Japanese media reported that the man was protesting the government's nuclear energy policy.
It is also reported that the drone was carrying "a small camera and a plastic bottle containing low level radioactive cesium."
The drone triggered fears of potential attacks using unmanned aerial devices. Prime Minister Shinzo Abe was travelling at the time.
Fukui is home to about a quarter of Japan's 48 workable reactors, which are currently all offline following the 2011 tsunami-triggered Fukushima plant disaster, the worst nuclear crisis since Chernobyl 25 years earlier. Abe's administration wants to restart as many of the idled plants as possible.
Yamamoto said he put radioactive sand in a container on the drone that he got from Fukushima, media reported.
The government's push to restart the reactors is unpopular among many Japanese, who view nuclear energy as too dangerous.