Tech majors such as Facebook, Google and Twitter have been sued by family members of the three victims of the 2 December, 2015 San Bernardino shooting.

They claim the companies allowed Islamic State (Isis) to spread propaganda freely on social media, provided material support to the group and enabled attacks like the one that took place in San Bernardino.

In a complaint filed in the US District Court in Los Angeles on Wednesday (3 May), seen by Reuters, the family members of Sierra Clayborn, Tin Nguyen and Nicholas Thalasinos alleged: "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."

"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 claims.

Authorities said Syed Rizwan Farook and his wife Tashfeen Malik, who killed 14 people and injured 22 others in the shooting, were inspired by Isis.

This is not the first instance of tech firms facing a lawsuit. After the San Bernardino shooting, ranked as the deadliest attack by Isis in the US, in June 2016, an American-born man, who pledged allegiance to Isis shot 49 people at the Pulse nightclub in Orlando, Florida.

In December the families of three men who died in the shooting sued Twitter, Google and Facebook in the federal court over charges similar to those of the California lawsuit.