European Commissioner Thierry Breton has issued public warnings to Mark Zuckerberg and Elon Musk that their social media platforms need to comply with European Union regulations about the spread of illegal content or face large fines and potential bans within the economic bloc.

On Wednesday, Breton joined the chorus of criticism against Musk’s X, formerly Twitter, for the platform’s failure to curb mis- and disinformation in the early days of the war between Israel and Hamas.

In an open letter posted on X, Breton said there were “indications” the social media site “is being used to disseminate illegal content and disinformation in the EU”.

“Let me remind you that the Digital Services Act sets very precise obligations regarding content moderation,” the letter said.

The EU’s Digital Services Act (DSA) lets regulators flag illegal content – like terrorist or child sexual abuse material – for removal and requires strict transparency and risk management processes.

Failure to comply with the DSA can result in fines of up to six per cent of global turnover and could potentially lead to temporary bans in the EU.

“Public media and civil society organisations widely report instances of fake and manipulated images and facts circulating on your platform in the EU, such as repurposed old images of unrelated armed conflicts or military footage that actually originated from video games,” Breton said in the letter addressed to Musk. “This appears to be manifestly false or misleading information.”

Musk replied to Breton, asking the European Commissioner to “list the violations … so that the public can see them”.

Breton’s responded by saying Musk was “well aware” of the various “reports on fake content and glorification of violence” on X and said it was “up to you to demonstrate that you walk the talk”.

“I still don’t know what they’re talking about,” Musk later wrote. “Maybe it’s in the mail or something.”

The next day, Breton addressed a letter to Meta CEO Mark Zuckerberg on the Twitter-like Bluesky platform (Instagram Threads is not currently available in Europe).

“Following the terrorist attacks carried out by Hamas against Israel, we are seeing a surge of illegal content and disinformation being disseminated in the EU via certain platforms,” Breton said.

“I would ask you to be very vigilant to ensure strict compliance with the DSA rules on terms of service, on the requirement of timely, diligent and objective action following notices of illegal content in the EU, and on the need for proportionate and effective mitigation measures.

“I urgently invite you to ensure that your systems are effective.”

Threads appears to be going through a period of growth with journalists and public figures flocking there in recent days in the hopes of finding a viable Twitter/X alternative.

But despite a similar visual appearance to X with its scrolling text-based feed, Threads has a tight content policy – searches for ‘covid’ turn up no results – and an algorithmic feed that, by design, doesn’t promote news.

Head of Instagram confirmed as much on Wednesday, saying that the platform isn’t “anti-news” but it also is “not going to amplify news”.

“To do so would be too risky given the maturity of the platform, the downsides of over-promising, and the stakes.”