小型无人机落日本首相官邸屋顶

Japanese authorities have launched an investigation after discovering a small drone on the roof of Prime Minister Shinzo Abe's office.

The four-propeller drone measured about 50 centimeters in diameter and was carrying a camera, a plastic bottle, and a flare-like device, according to national broadcaster NHK.

Several media outlets also reported the drone was decorated with a radioactive symbol, and the Kyodo news agency reported a small amount of radiation was measured on the craft.

Television footage showed dozens of police officers hovering around the drone, which was covered by a blue tarp.

It is not clear who sent the drone or what their motive may have been. There have been no reported injuries. Prime Minister Shinzo Abe was away from his office at the time, attending a conference in Indonesia.