A man was arrested for flying a small drone carrying radioactive element cesium over the roof of Japanese Prime Minister Shinzo Abe's office, authorities said on Saturday.
Yasuo Yamamoto, 40, was arrested on Friday over suspicion of forcible obstruction of business, Xinhua news agency reported.
The man said his intention to fly the drone was to protest against the Japanese government's nuclear energy policy.
The drone was found on the roof of the prime minister's office on Wednesday.
The flying device, about 50 cm in diameter, was equipped with a global positioning system (GPS), a small camera and a bottle of liquid with a sticker reading "radioactive".
The police later detected small trace of radioactive cesium in the liquid.
According to government officials, they have started considering legislation to regulate drone flights over important offices.