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 . Dozens of police investigators were dispatched to the roof to investigate the origin of the drone , which had four propeller and was 50 centimeters ( 20 inches ) wide . Police say the drone was equipped with a small camera , smoke flares and a plastic bottle containing small traces of a radioactive material believed to be cesium , a common byproduct of nuclear reactors . Cesium was also discovered in areas around the failed Fukushima Daiichi nuclear plant after its 2011 meltdown . Investigators suspect the cesium was placed in the bottle . The amount inside is not immediately harmful to humans . Chief Cabinet Secretary Yoshihide Suga said the discovery is raising concerns about terrorism . `` There might be terrorism attempts in the future at the Olympics and G7 Summit using drones , '' Suga said . `` So we need to examine and review continuously the way small unmanned vehicles like drones should be operated and how to cope with the threat of terrorism from drones . The government will do all that we can to prevent terrorism . '' Japanese law restricts drone flights around airports to prevent problems with aircraft , but there are no flight restrictions for most of Tokyo , including the Prime Minister 's residence and local and federal government buildings . Abe was not in his office at the time . He is in Indonesia , attending the Asian-African Conference . CNN 's Elizabeth Joseph , Joshua Berlinger and Josh Levs contributed to this report .
The drone is sparking terrorism concerns , authorities say . It was equipped with a bottle containing radioactive material . Score: 6