Hackers purporting to be supporters of Islamic State knocked out channels belonging to French public television station TV5Monde and posted material on its social media feeds to protest French military action in Iraq.
President Francois Hollande's government branded the cyber attacks, which started late on Wednesday, a "vile and cowardly" affront to freedom of expression and began an investigation, promising to track down those responsible.
Yves Bigot, head of the TV5Monde station, said the assault caused its 11 channels to go temporarily off air and also hit its websites. The network broadcasts news and entertainment programmes in French on 11 channels around the world, and is 49 percent owned by state-backed broadcaster France Televisions.
French news agency AFP said the hackers posted documents on TV5Monde's Facebook page purporting to be the identity cards of relatives of French soldiers involved in anti-Islamic State operations, and threats against the troops.
The Facebook page was back up on Thursday but the main website remained down.
The French Foreign Ministry confirmed the attack had been claimed by individuals purporting to back Islamic State. French foreign, interior and culture ministers visited the channel's offices in Paris and pledged to identify those responsible.
"We are faced with determined terrorists, and we are determined to fight them," Interior Minister Bernard Cazeneuve said, adding that cybersecurity measures would be reinforced.
A judicial source said a preliminary investigation had begun. Culture Minister Fleur Pellerin called for a meeting with the heads of major broadcasters to assess weak spots and how best to deal with them.
France is part of the international coalition carrying out strikes against Islamic State insurgents in Iraq. Its aircraft carrier Charles de Gaulle joined operations there in February.
© Thomson Reuters 2015