PARIS — Hackers claiming allegiance to the Islamic State group seized control of a global French television network, simultaneously blacking out 11 channels and taking over the network’s website and social media accounts. The attack appeared to be an unprecedented step in the extremist group’s information warfare tactics.

The hackers briefly cut transmission of 11 channels belonging to TV5 Monde and took over its websites and social media accounts starting Wednesday night. The channel’s director, Yves Bigot, said the attack continued into Thursday. He told RTL radio that the network has restored its signal but can only broadcast recorded programs.

The Islamic extremist group has claimed complex hackings before, but experts and a French official said the ability to black out a global television network represented a new level of sophistication for the group. The Paris prosecutor’s office said Thursday it has opened a terrorism investigation into the attack.

Bigot said he was shaken when he saw the black screen across the network’s broadcasts “and when we discovered the sense of the message appearing on our social media and our websites, it both allowed us to understand what was happening and obviously worried us.”