Story highlights The drone is sparking terrorism concerns, authorities say

It was equipped with a bottle containing radioactive material

It was discovered as a court approved a plan to restart two Japanese nuclear reactors

Tokyo (CNN) A bizarre and alarming discovery is raising concerns in Japan about the potential for terrorism involving drones.

A drone carrying traces of a radioactive material was found on the rooftop of Japan's equivalent to the White House on Wednesday, police and government officials said.

The discovery came on the same day a Japanese court approved a government plan to restart two reactors at the Sendai nuclear power plant in Kagoshima prefecture, more than four years after the Fukushima Daiichi nuclear disaster.

Prime Minister Shinzo Abe 's push to restart the reactors is unpopular among many Japanese, who view nuclear energy as too dangerous.

A staff member spotted the drone Wednesday morning on the roof of Abe's residence, Tokyo Metropolitan Police said.