More than 100 police, firefighters and officials were called to the shrine's public bathroom on Monday after a small fire was reported to authorities. Tokyo Fire Department said the blaze was already out by the time they arrived.

Police, however, said they found possible traces of an explosion, as well as batteries and wires at the shrine, leading authorities to believe that the incident could have been politically motivated.

Tensions over war shrine

The controversial Yasukuni shrine honors Japan's war dead, including those executed as war criminals. Japan's neighbors - particularly China and North and South Korea, who were victims of atrocities and aggression during the Second World War - remain extremely critical of the memorial.

During the 1930s and 1940s, Japan was responsible for a host of atrocities in the Asian-Pacific region, including forced labor, the use of "military comfort women," torture of prisoners of war, mass killings and human experimentation.

Visits to the shrine by Japanese politicians have also been frowned upon. While some Japanese lawmakers have insisted on making an official visit on the principal of patriotism, others believe that in doing so, they would glorify Japan's historical military mistakes.

ksb/kms (Reuters, AP, dpa)