Tokyo, April 23 (IANS): Japanese authorities are exploring the possibility that radioactive cesium found in a drone that landed on Prime Minister Shinzo Abe's residence could be from the Fukushima nuclear power plant, Efe news agency reported citing investigators.

Given that the isotopes detected in the drone are not found in nature and are a product of nuclear fusion, authorities believe they could be the result of emissions released during the 2011 Fukushima nuclear disaster, sources from the Tokyo police told Kyodo news agency on Thursday.

The accident at the Fukushima plant triggered by the earthquake and tsunami on March 11, 2011, was the worst since the Chernobyl meltdown in Ukraine in 1986.

It forced the evacuation of 70,000 people from the area and seriously affected agriculture, fisheries and local livestock.

An unmanned aerial vehicle with a 50-cm wingspan and of unknown origin was found near the heliport on the roof of Abe's residence in Tokyo on Wednesday.

Abe is currently in Jakarta, Indonesia, attending the Asian-African summit.

The device was equipped with a camera and a container of liquid in which were detected radioactive elements of too low intensity to pose a health risk.

Pasted on the drone was a sticker with the tri-foil symbol for radiation and the word "radioactive".

The drone model is sold in several parts of Japan.

Police said the drone must have landed on the roof of the residence after it was last inspected by security personnel on March 22.

The discovery of the drone has heightened concern about the lack of regulation in Japan for drone flights around buildings and facilities with restricted access.