An explosion at the Yasukuni Shrine for the war dead in Japan's capital Tokyo on Monday hit a public restroom near the south gate of the shrine.
The Tokyo Metropolitan Police Department has launched an investigation into the incident, public broadcaster NHK reported.
No injuries have been reported but the ceiling, floor and a wall of the toilet were damaged, local media reported.
Police said investigators discovered batteries and wires at the scene and also four iron pipes.
Yasukuni Shrine began its annual Festival of First Fruits and there were more visitors than usual.
Police suspect the blast may have been a deliberate attempt to attack the shrine.
Yasukuni shrine honours Japan's war dead including military and political leaders convicted of war crimes by an international military tribunal after World War II.