The acid attack occurred between the Bastille and Gare de Lyon metro stations in Paris at about 8 a.m. on 15 February after a disagreement erupted between two individuals, France Info reported referring to a police source.
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One person was critically injured in the attack, suffering burns to his hands and face, and is said to be in a life-threatening condition, Le Parisien clarified.
The perpetrator is on the run, while a police operation is underway at the Gare de Lyon station.
The incident comes just two days after Le Parisien reported that a woman and a man, travelling on line 11 of the Paris metro, suffered burns from sulfuric acid in a bottle. It remains to be determined whether it was inadvertently left behind on the train.