The hacking group Anonymous has declared war against the Islamic State for carrying out strategic bombings that killed 129 people in Paris on Saturday.

In a video posted on YouTube, the cyber activists said they will launch their "biggest operation ever" - warning the depraved terror group to "expect us", reports The Express.

Behind their trademark Guy Fawkes mask, a spokesman said in French: "Anonymous from all over the world will hunt you down. You should know that we will find you and we will not let you go.

"We will launch the biggest operation ever against you."

The masked man told the savage terrorists to expect "massive" cyber attacks, adding: "War is declared. Get prepared.

"The French people are stronger than you and will come out of this atrocity even stronger."

After the Charlie Hebdo attacks in January, Anonymous started publishing a list of Twitter accounts it says are spreading Islamic State propaganda.

Over the weekend IS claimed responsibility for the latest attacks in Paris which have so far claimed the lives of 129 people.

The terrorists targeted six different locations in the French capital, including Stade de France where president Francois Hollande was watching the national team play a friendly match against Germany.

Gunmen also attacked restaurants and cafes.

Most of the victims came from the Bataclan theatre where rock band Eagles of Death Metal were performing when gunmen burst into the concert hall and fired into the crowd.

89 people were killed there - and there are still 26 victims yet to be identified, while a further 99 people are critically injured following the bomb and gun attacks.