A drone marked with a radioactive sign has been found on the roof of Japanese Prime Minister Shinzo Abe's office and tested positive for a "minuscule" amount of radiation.

The radiation was so low it was not harmful to humans but the bomb squad was called in to take away the drone which was carrying a small camera and a water bottle.

Mr Abe was in Indonesia attending an Asia-Africa summit.

It was not immediately clear who sent the drone or why. But a Japanese court has approved the restart of a nuclear power station in the southwest of the country, rejecting worries about nuclear safety in the wake of the 2011 Fukushima radiation disaster.

The ruling was a boost for Mr Abe who wants to reboot nuclear power to help cut reliance on expensive fossil fuel imports.

An official at the premier's office found the drone which was around 20 ins in diameter. No-one was injured.