Elon Musk's X has launched legal action against a string of companies after they stopped advertising on the social network.

The tech giant, formerly known as Twitter, alleges the firms unlawfully conspired to boycott the site and caused it to lose "billions of dollars" in revenue.

The lawsuit was filed in Texas against the World Federation of Advertisers and member companies British multinational Unilever, food giant Mars, CVS Health and Danish renewable energy company Orsted.

Musk wrote on X: "We tried peace for two years, now it is war."

It comes after advertising revenue at X slumped after Musk bought and renamed the social network for $44bn (£35bn) in 2022.

Within days of taking over, Musk made thousands of employees redundant - including many moderation staff tasked with removing harmful content.

Companies also halted advertising on the site in November 2023 following concerns their content was showing up next to pro-Nazi posts, with X's owner also accused of spreading hate speech.

Musk later apologized for endorsing an antisemitic conspiracy theory but also told advertisers to "go f*** yourself".

The tech billionaire has come under growing criticism over his running of the site, which most recently has been blamed for failing to tackle misinformation spread during the riots in England.

The lawsuit claims the advertisers - acting through a World Federation of Advertisers initiative called Global Alliance for Responsible Media (GARM) - colluded in a way that violated US anti-trust laws.

The scheme was launched in 2019 to "help the industry address the challenge of illegal or harmful content on digital media platforms and its monetization via advertising".

X is seeking unspecified damages, as well as a court order against any continued efforts to conspire to withhold advertising spending.

It said it has applied brand-safety standards that are comparable to those of its competitors and that "meet or exceed" measures specified by GARM.

X's chief executive Linda Yaccarino said: "People are hurt when the marketplace of ideas is constricted. No small group of people should monopolize what gets monetised."

Professor Christine Bartholomew, an anti-trust expert from Buffalo University, said X would have to prove there was an agreement to boycott joined by each advertiser, which she described as "no small hurdle".

She added that even if the case was successful, Musk could not legally force companies to advertise on X.

The firms accused by X are yet to comment on the lawsuit.

However, Unilever, which owns brands including Dove, Persil and Wall's, told a hearing in Congress last month it only advertised on platforms that did not harm its brand.

The company's president Herrish Patel said in a statement: "Unilever, and Unilever alone, controls our advertising spending. No platform has a right to our advertising dollar."