They said that they were avenging the prophet , Paris Match reported . Security forces have warned of a rising threat from Islamist extremists . In 2004 , the bombings of commuter trains killed 191 people and injured 1,800 . No responsibility has been claimed for the attack on Charlie Hebdo . But it has in the past been subject to criticism over its coverage of Islam .
They said that they were avenging the prophet , Paris Match reported . Security forces have warned of a rising threat from Islamist extremists . No responsibility has been claimed for the attack on Charlie Hebdo . But it has in the past been subject to criticism over its coverage of Islam .