Security has been tightened in Tokyo ahead of the G7 summit scheduled to be held in May, authorities said.
The Metropolitan Police Department on Tuesday deployed hundreds of additional officers at railway stations and other crowded public spaces, public broadcaster NHK reported.
Police said terrorists could target Tokyo as well as Ise-Shima where the two-day summit will begin on May 26.
Riot squads are stationed at checkpoints at the Haneda airport.
Sniffer dogs are being used to search for explosives in Ueno Park where people were gathering to view the cherry blossom.
