WhatsApp has launched a lawsuit against an Israeli surveillance firm, alleging that it was behind cyber-attacks on more than 100 human rights activists, lawyers, journalists and academics.

The messaging firm claims that the NSO Group, headquartered in Herzliya, violated US law in an “unmistakable pattern of abuse”, the Guardian reports.

WhatsApp claimed in the lawsuit, which it filed in the US state of California, that technology sold by NSO was used to target the mobile phones of users in 20 countries over a two-week period.

It did not disclose who it alleged was using the technology, but area codes for a number of phones that had been targeted indicated a focus on people in Mexico, Bahrain and the United Arab Emirates.

A WhatsApp spokesman said: “This is the first time that an encrypted messaging provider is taking legal action against a private entity that has carried out this type of attack against its users.

“In our complaint, we explain how NSO carried out this attack, including acknowledgement from an NSO employee that our steps to remediate the attack were effective.

“There must be strong legal oversight of cyber-weapons like the one used in this attack to ensure they are not used to violate individual rights and freedoms people deserve wherever they are in the world.

“Human rights groups have documented a disturbing trend that such tools have been used to attack journalists and human rights defenders.”

NSO Group, which sells its surveillance technology to governments all over the world, said in a statement on Tuesday that it disputed the claims in the WhatsApp lawsuit in the “strongest possible terms” and “will vigorously fight them.”

NSO Group added that its technology was used by intelligence and law enforcement agencies in lawful antiterrorism efforts and crime-fighting, and it “has helped to save thousands of lives over recent years.”

WhatsApp reportedly worked with Citizen Lab, an academic research group based at the University of Toronto, to identify the targets of the cyber-attacks and the technology that was used.

John Scott-Railton, a senior researcher at Citizen Lab, said the legal action was “a major positive step forward for human rights protections online and will absolutely set a precedent.”

He added: “While telling the public it is concerned about human rights, the commercial spyware industry has attempted to carve out an unaccountable space for itself, whereby virtue of its proximity to governments, it claims it is acting lawfully, yet prefers to disclaim any responsibility for that behaviour when it suits them.”