A 41-year-old man was burned early Thursday after being pushed onto the tracks of the Paris metro by a homeless man, raising concerns about safety in the underground system, police said.
The suspect, who was placed in preventive detention, told police he wanted "revenge" without explaining further.
The injured man was taken to hospital, and doctors said his burns were not life threatening.
The incident occurred at the Bercy station in eastern Paris, near the French finance ministry and a major sports stadium.
In March, a homeless man was crushed to death by a Paris metro train after falling on the tracks during a fight with two Chilean tourists. A month before, a man was pushed to his death under an oncoming train by a deranged assailant.