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A man and a woman sustained burns on Tuesday night at a Tokyo subway station with the perpetrator still at large, the incident occurring amid tightened security as the Tokyo Paralympics opened the same day.
A suspect threw what is believed to be sulphuric acid and fled the scene, police and local media said on Wednesday.
The 22-year-old man sustained injuries to his face and shoulder while the 34-year-old woman suffered burns on her legs.
According to the reports the attack happened shortly after 9pm at Tokyo Metro Co.'s Shirokane Takanawa Station in the capital's Minato Ward.
One of the victims, a businessman, sustained burns to his face after the suspect sprayed liquid at him on an escalator, a police spokesman told the local media.
Violent crime is comparatively rare in Japan, which has strict gun laws, although there are occasionally attacks involving other weapons.
During the Olympics earlier in August, 10 people were wounded — one of them seriously — in a stabbing attack on a commuter train in Tokyo.
The suspect later handed himself in after fleeing the scene.Around 60,000 police officers are being deployed for the Olympics and Paralympics, according to Japanese media.
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