TOKYO - A man was arrested for flying a small drone carrying radioactive cesium to the roof of Japanese Prime Minister Shinzo Abe's office last week, local media reported Saturday.

Yasuo Yamamoto, 40, was arrested on suspicion of forcible obstruction of business and has admitted to them, police investigators said.

The man was quoted by Kyodo News Agency as saying that his intention to fly the drone was to protest against Japanese government's nuclear energy policy.

On Wednesday, a drone was found on the roof of the prime minister's office. The flying device, about 50 centimeters in diameter, equipped with a global positioning system and a small camera as well as a 10cm bottle of liquid with a sticker showing a radioactivity symbol and the word "radioactive."

The police later detected small trace of radioactive cesium in the liquid. Prime Minister Shinzo Abe was in Indonesia to participate the Asian-African summit at that time.

According to government officials, they have started considering legislation to regulate drone flights above important facilities.

"We need to immediately establish legislation on drone usage," Chief Cabinet Secretary Yoshihide Suga said Friday at a meeting.