Family members of three victims of the December 2015 shooting rampage in San Bernardino, California, have sued Facebook, Google and Twitter, claiming that the companies permitted Islamic State to flourish on social media.

The relatives assert that by allowing Islamic State militants to spread propaganda freely on social media, the three companies provided "material support" to the group and enabled attacks such as the one in San Bernardino.

"For years defendants have knowingly and recklessly provided the terrorist group ISIS with accounts to use its social networks as a tool for spreading extremist propaganda, raising funds and attracting new recruits," family members of Sierra Clayborn, Tin Nguyen and Nicholas Thalasinos charge in the 32-page complaint, which was filed in U.S. District Court in Los Angeles on Wednesday.

"Without defendants Twitter, Facebook and Google (YouTube), the explosive growth of ISIS over the last few years into the most feared terrorist group in the world would not have been possible," the complaint said.