A 40-year-old Japanese man admitted he landed an unmanned drone in central Tokyo carrying radioactive sand atop Prime Minister Shinzo Abe's office to protest nuclear power, police said Saturday.

The drone, which had a sign on it saying it was radioactive, was carrying a camera and plastic container with sand contaminated with radioactive cesium, Japanese media said. The police said the radiation was low and did not pose a threat. The stunt initially brought fears of a terrorist attack.

Yasuo Yamamoto, who is unemployed, faces a maximum three years in prison if convicted on charges of obstruction of official business. Local media reported that the police said the landing was a protest against nuclear power.

Abe is pushing to restart Japan's nuclear reactors which are offline in the wake of the Fukushima disaster caused by a tsunami in 2011. Public broadcaster NHK said the sand the drone was carrying came from an area near the Fukushima meltdown.

The drone was discovered Wednesday when new employees were taking a tour of the roof. It was believed to have landed there two weeks ago.

“I was operating the drone around 3:30 in the morning on April 9 to express my opposition to nuclear power generation,” police quoted the alleged drone operator as saying.

The Asahi Shimbun said the man surrendered to police on Friday. He allegedly had some of the sand with him, and he was said to have brought the drone's controller, too.

Police said the drone was a modified Phantom 2 produced by DJI of China.