The European Union's industry commissioner Thierry Breton has opened an investigation into X, the first under new EU tech rules, after earlier reprimanding the social media platform, TikTok and Meta for not doing enough to tackle the spread of disinformation following Hamas' attacks on Israel.
All three platforms have seen a surge of false content about the conflict, with disinformation appearing to be most prevalent on X, social media researchers said.
Mr Breton's move ramps up the pressure on TikTok and Meta - the owner of Facebook - to remove illegal and harmful content from their platforms in order to comply with the Digital Services Act (DSA).
The DSA, which came into force last November, forces large online platforms and search engines to do more to tackle illegal content and risks to public security, and protect their services against manipulative techniques.
X Chief Executive Linda Yaccarino said earlier that the platform had removed hundreds of Hamas-affiliated accounts and taken action to remove or label tens of thousands of pieces of content since the attacks, in response to a letter from Mr Breton.
"We have sent @X a formal request for information, a first step in our investigation to determine compliance with the DSA," Mr Breton said in an X post.
The platform declined to comment.
It has until 18 October to provide details on how its crisis response protocol is activated and functions, and until 31 October on other issues.
A move by X owner Elon Musk to cut off free academic access to a data tool earlier this year is making it more challenging to track keywords and hashtags, forcing researchers to manually sift through content to trace disinformation, researchers said.
Since taking over the platform, Mr Musk has slashed the workforce to roughly 1,500 from 7,500 employees to cut costs, including many who worked on content moderation, identifying and taking down coordinated propaganda campaigns and curating reliable content.
X has also lost two heads of trust and safety and one head of brand safety, who worked to prevent ads from appearing next to harmful content.
Earlier, Mr Breton gave TikTok CEO Shou Zi Chew 24 hours to step up efforts to remove illegal and harmful content from the short video app.
Mr Breton's warning in a letter to Mr Chew follows similar letters to Mr Musk and Meta Platforms' Mark Zuckerberg earlier this week.
Mr Breton subsequently posted the letter on social media platform Bluesky.
He said he had indications that TikTok, owned by Chinese conglomerate ByteDance, was being used to disseminate illegal content and disinformation in the EU after the Hamas attacks.
"Given that your platform is extensively used by children and teenagers, you have a particular obligation to protect them from violent content depicting hostage taking and other graphic videos which are reportedly widely circulating on your platform without appropriate safeguards," he said.
The EU industry chief said rules on content moderation were clear in the DSA and spelt out certain obligations in his letter.
X CEO Linda Yaccarino said the service had redistributed resources and refocused internal teams to address the rapidly evolving situation, without specifying the changes.
She added that the company assembled a leadership group to assess the situation shortly after the attacks.
"We wish to reiterate that we welcome further engagement with you and your team, including a meeting, to address any specific questions and look forward to receiving further specifics to which we can respond" Ms Yaccarino said in a letter to Mr Breton, posted on X.
The platform has responded to more than 80 take-down requests received in the EU within required the timeline and has not received any notices from Europol regarding illegal content on the platform, the letter states.
Breaches of the act can cost companies as much as 6% of their global turnover.
