Twitter, Google and Facebook are being sued for knowingly aiding ISIS by families of some of the victims of a terrorist attack in San Bernarndino, California that left 14 people dead.

The relatives claim the tech giants have allowed the group to build a major online presence and push its extremist beliefs, as well as enlist recruits and promote attacks like the mass shooting in San Bernardino, California.

‘Without defendants Twitter, Facebook and Google (YouTube), the explosive growth of IS over the last few years into the most feared terrorist group in the world would not have been possible,’ the suit alleges.

The lawsuit was filed on Wednesday at the US District court in Los Angeles by the families of Sierra Clayborn, Tin Nguyen and Nicholas Thalasinos, three of the 14 people gunned down on December 2, 2015 by Syed Rizwan Farook and his wife, Tashfeen Malik.

Syed Rizwan Farook, left, and his wife, Tashfeen Malik, right, killed 14 people in the December 2015 shooting. Victims of the shooting are now suing tech giants Facebook, Twitter and Google for allegedly allowing the Islamic State to build a large online terrorist that helped inspire terrorists like Farook an d his wife

The couple targeted a Christmas party being held in a banqueting room at San Bernardino County Department of Public Health. Twenty-two other people were injured in the shooting.

‘For years, Defendants have knowingly and recklessly provided the terrorist group IS with accounts to use its social networks as a tool for spreading extremist propaganda, raising funds, and attracting new recruits,’ reads the complaint, filed by lawyers Keith Altman and Theida Salazar.

‘Even if Farook and Malik had never been directly in contact with IS, its use of social media directly influenced their actions on the day of the San Bernardino massacre,’ the lawsuit added.

FBI Director James Comey said immediately after the shooting that although there was no evidence the couple was directed by a terrorist group, there were clues pointing to ‘potential inspiration by foreign terrorist organisations.

‘The Internet allows the opportunity for people to consume poison and radicalise,’ he added.

The internet giants have faced growing outrage over the material they provide access to, including child abuse images and instructions for terrorist acts - which Google profited from through YouTube adverts - as well doing little to prevent online bullying.

And this week Facebook bowed to pressure to crack down on live broadcasts of murders and suicides on the social network.

The web giant is to hire 3,000 more staff to police what users post, joining 4,500 already in place to stamp out violence, hate speech and child abuse images.

The company was forced to act after an outcry over a number of disturbing incidents broadcast via Facebook Live, its ‘streaming’ service that lets users put whatever they like directly on the network.

A recent survey by the NSPCC found 80 per cent of 11 to 18-year-olds believe social media firms fail to protect them from harmful content.

According to the Los Angeles Times, the lawsuit contends the companies are liable for aiding and abetting acts of international terrorism, wrongful death and providing material support to a designated foreign terror group among other charges.

The legal action mirrors similar lawsuits filed by families following deadly attacks at an Orlando nightclub last June and the slaying of five police officers in Dallas a month later. The father of a victim from the Paris massacre sued the same three companies for providing a platform to ISIS.

The suits challenge the interpretation of the Communications Decency Act, a US law that states that Internet platforms are not liable for what their users post on their sites.

While legal experts claim the lawsuit is unlikely to succeed in court and the statute has protected social media sites in the past, lawyers are claiming the secretive algorithms used to curate content can be open to abuse.

In previous cases, Google, Facebook and Twitter have said they are sympathetic to victims of such attacks but are not liable for what happened.

Asking for the Orlando lawsuit to be dismissed in court papers filed last week, the companies argued that accepting such an ‘unbounded theory’ behind the Pulse nightclub attack that left 49 dead ‘would have staggering consequences, exposing every online platform to possible liability for terrorist violence anywhere in the world, at any time, simply because terrorists who committed the attack may have been loosely affiliated with some of the platforms’ billions of users.’

A Facebook spokesperson said the company was ‘committed to providing a service where people feel safe when using Facebook.

‘Our Community Standards make clear that there is no place on Facebook for groups that engage in terrorist activity or for content that expresses support for such activity and we take swift action to remove this content when it’s reported to us. We sympathize with the victims and their families,’ the statement added.

Twitter and Google have also said they are working to prohibit the promotion of terrorism. Among the initiatives is a shared industry database of unique digital ‘fingerprints’ linked to terrorism.