A bomb exploded at Tokyo’s Yasukuni Shrine on Monday at around 9am Hong Kong time.
A dry battery device was placed in a male toilet on the grounds of the controversial shrine, according to local media.
The Tokyo fire department told Sankei News that the resulting fire was put out quickly.
Public broadcaster NHK reported that the explosion created a 30 centimetre hole. No one was injured though, as it is Niiname-sai – Labour Thanksgiving Day – there were more visitors to the shrine than usual.
The police are investigating the incident as a terror attack.
The Shinto shrine in Chiyoda honours the war dead, including those who died in WWII. It has long been a source of contention between Japan and its Asian neighbours, who believe it glorifies the county’s militarist past.
Additional reporting: Tom Grundy.