A man was arrested after flying a drone carrying radioactive sand onto the roof of the Japanese prime minister's office.

Police in Tokyo said Yasuo Yamamoto, 40, who protesting over the Japanese government's nuclear energy policy, had turned himself in.

Prime Minister Shinzo Abe was out of the country at the time and the levels of radioactive material - thought to be caesium - were said to be too low to be harmful to human health.

However the landing of the drone triggered a major security alert and has raised fears over extremists using the remote-controlled device to carry out attacks.

Officials in Japan are currently looking into regulating low-altitude drone flights as the devices become more popular.