Tech firms will be required to shield internet users from state-sponsored disinformation posing a threat to UK society and democracy, under changes to a landmark online safety bill.

The legislation will require social media platforms, video streaming services and search engines to take action to minimise people’s exposure to foreign state-backed disinformation aimed at interfering with the UK. Such content would, for instance, include incidents such as the video of Ben Wallace being prank-called earlier this year by Russian hoaxers pretending to be the Ukrainian prime minister.

The culture secretary, Nadine Dorries, said the Ukraine invasion had underlined Russia’s willingness to use social media to spread lies and disinformation.

“We cannot allow foreign states or their puppets to use the internet to conduct hostile online warfare unimpeded,” she said. “That’s why we are strengthening our new internet safety protections to make sure social media firms identify and root out state-backed disinformation.”

A Russian prankster duo called Vovan and Lexus claimed responsibility for the Wallace call, which took place in March. The pair were suspected of links to Russia’s security services, which they denied. A clip of the call was posted on YouTube but then taken down by the Google-owned video service.

The amendment will be added to the forthcoming national security bill, which undergoes parliamentary scrutiny by a committee of MPs next week. In its current form the online safety bill, which is expected to pass into law by the end of the year, already requires tech firms to take action on state-sponsored disinformation that harms individuals – such as threats to kill.

“Disinformation is often seeded by multiple fake personas, with the aim of getting real users, unwittingly, then to ‘share’ it,” said security minister Damian Hinds. “We need the big online platforms to do more to identify and disrupt this sort of coordinated inauthentic behaviour. That is what this proposed change in the law is about.”

The amendment will add a new disinformation offence to the list of priority offences in the bill, which tech firms are required to prevent proactively. These include terrorism, child sexual abuse and fraud offences. Breaches of the act would be punished by the communications regulator, Ofcom, with fines of up to £18m or 10% of a company’s global turnover, which could run into billions of pounds for some of the US-based tech giants.

The government amendment was announced as the digital, culture, media and sport (DCMS) committee proposed changes to the bill that would curb the influence of the culture secretary in shaping new rules for tech firms. The amendments proposed by the committee scrap the secretary of state’s right to direct or block Ofcom in issuing codes of practice, including on dealing with terrorist and child sexual exploitation content, before parliament considers them.

“A free media depends on ensuring the regulator is free from the threat of day-to-day interference from the executive,” said Julian Knight MP, the committee’s Conservative chair. “The government will still have an important role in setting the direction of travel, but Ofcom must not be constantly peering over its shoulder answering to the whims of a backseat-driving secretary of state.”

A DCMS spokesperson said: “Technology is changing rapidly and while the bill will maintain Ofcom’s independence it gives democratically elected governments and parliament appropriate oversight to address any issues that fall outside Ofcom’s remit in the future.”