Four teenagers were wounded, two of them seriously, after an axe was used during a fight on a suburban train outside Paris, French police sources have said.
One of the victims, all aged 16 or 17, had a hand cut off and another had their skull split open. The main suspect in the incident was later arrested.
The two other victims were less seriously injured in the altercation, which a police source said broke out at about 8am (0700 GMT) as the teenagers were on their way to secondary school.
It was not immediately clear what triggered the fight, in which weapons including the axe, a knife, a samurai sword and baseball bats were used.
All the wounded were taken to hospital and none had life-threatening injuries, the source added.
The main suspect, 16, was later arrested at his home and held in custody, another police source said.
An axe was found and confiscated during the search, they added.
The incident happened while the RER suburban express train was at the station of Ozoir-la-Ferrière south-east of Paris.
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As the train was being held at the station, the violence did not affect traffic on the RER E line, which runs east-west through Paris and its suburbs, state rail operator SNCF said.