A suspected explosive device damaged a bathroom at Tokyo's Yasukuni Shrine on Monday, but no one at the controversial war memorial was hurt, officials and news reports said.
Police received reports of a loud bang and smoke rising near the public bathroom inside the shrine on Monday morning, a spokesman said.
Public broadcaster NHK said the small blast occurred as a larger-than-usual number of people were visiting the shrine for an annual harvest festival.
Police found the ceiling and wall of the bathroom damaged and burned, NHK said, adding that they also found a battery and wire there.
A bomb unit attended the scene and police have now launched an investigation into whether the incident was a targeted attack.
"Fortunately, no one was injured," a shrine official said, adding that it had not received any threat in connection with the explosion.
The incident came as Japanese authorities were beefing up security in the capital after the Paris attacks that killed 130.
"I was a bit surprised as (terrorism) just occurred in France," a visitor to the shrine told NHK.
A South Korean national was charged two years ago for attempting to set fire to the shrine, while a man was also arrested in December for suspected arson there, the broadcaster said.
The shrine honours millions of Japan's war dead, but also controversially includes several senior military and political figures convicted of war crimes.
Visits to the shrine by senior Japanese politicians routinely draw an angry reaction from Beijing and Seoul, which see it as a symbol of Tokyo's military past.
An attached museum portrays Japan more as a victim of US aggression in WWII and makes scant reference to the extreme brutality of invading Imperial troops when they stormed through Asia.
In October, three state ministers from Prime Minister Shinzo Abe's cabinet paid homage to mark the autumn festival.
The nationalist Abe has visited the shrine once during his time in office, in December 2013. That sparked anger among Japan's neighbours and a diplomatic slap on the wrist from the US, which said it was "disappointed".
Chinese social media users were quick to laud the bomber.
"I don't know who blew it up, but they blew it up well," read one comment on micro-blogging site Sina Weibo, with another adding: "You blew it up well. That's worthy of celebrating!"
Another user said: "If it were another place, I'd say 'don't let it happen again', but it's Yasukuni, so I just laughed."