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 .
Attackers shouted that they were avenging the prophet , Paris prosecutor says . Security officials 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 threats over its coverage of Islam .