A drone carrying trace amounts of radiation landed on the roof of Japanese Prime Minister Shinzo Abe's office on Wednesday. No one has yet claimed responsibility for the action, but it coincides with a key victory for Abe in his push to restart Japan's nuclear power program, which has remained dormant since the 2011 Fukushima disaster.

The drone was reportedly equipped with a camera, a radiation sign, and was carrying a water bottle. An official with the prime minister's office told local media that the radiation levels were low enough not to be a threat to humans. The area was covered in blue tarpaulin and the aircraft was carried away by police officers.

"This situation concerns the center of Japanese government, the prime minister's office, and we will take every necessary step, including a detailed investigation by police," Yoshihide Suga, chief cabinet secretary, told reporters.

The case represents the latest in several high-profile uses of the technology that have stirred controversy. In February, a drone that landed on the White House lawn caused a security scare, though it was later deemed to be an accidental breach of the presidential estate. Since last year, several drones have been spotted over French and Belgian nuclear power plants, and they remain a mystery.

Abe was out of the country, attending a summit of Asian and African leaders in Indonesia. So he was absent for this drone, but also a landmark win in his push to reinvigorate Japan's nuclear power industry.

Wednesday also marked a decision in Kagoshima district court that is likely to have national ramifications. The court rejected an injunction by local residents opposed to the restart of the first two nuclear reactors which the Nuclear Regulation Authority, set up after Fukushima, has approved to restart operation.

"We will not let our emotions be swayed by any short-term results and we will fight until we get rid of all nuclear reactors in Japan," said Hiroyuki Kawai, a lawyer representing the residents in the case, who promised additional legal challenges would be brought.

"The government respects the decision to resume plants that it considers meeting safety standards, while placing top priority on safety over any other factor," Suga said, when asked about the government's reaction to the decision.

The ruling opens the door to the resumption of a multi-billion dollar nuclear power industry, which has essentially been in a state of hibernation. All 48 of Japan's power plants were shutdown in the aftermath of the Fukushima disaster, with the last one being switched off in September 2013.

Abe and his Liberal Democratic Party have long believed in restarting the country's reactors, having labeled nuclear power a fundamental "base-load power" for the country. Now after winning a snap election in December, the government has the political capital to push through the unpopular policy.

A poll conducted on the eve of the election by public broadcaster NHK showed 40 percent of Japanese people opposed the restarts, while only 24 percent supported them. Public doubt over safety standards and the ability of the country's nuclear watchdog has been stoked by errors made during the Fukushima disaster and restarting the reactors has become a sensitive political issue.

But without the reactors, Japan faces an unstable energy future. The country is now dependent on imports for 96 percent of its primary energy needs, a figure that would be reduced by 16 percent if the existing reactors were switched back on.