The raid by the Paris prosecutor's cybercrime unit on Tuesday and Musk's summoning - which could further increase tensions between Europe and the US over Big Tech and free speech - are linked to a year-long investigation into suspected abuse of algorithms and fraudulent data extraction by X or its executives.
Britain's privacy watchdog, meanwhile, also kicked off a formal investigation into Musk's artificial-intelligence chatbot Grok over the processing of personal data and its potential to produce harmful sexualised images and video content.
"The Paris Public Prosecutor's Office is plainly attempting to exert pressure on X's senior management in the United States by targeting our French entity and employees, who are not the focus of this investigation," X said in a statement.
"The Prosecutor's Office has ignored the established procedural mechanisms to obtain evidence in compliance with international treaties and X's rights to defend itself."
Referring to the raids, Musk said in a post on X, "This is a political attack."
The Paris prosecutor's office said it had broadened the scope of its investigation following complaints over the functioning of Grok.
The French probe will now also investigate alleged complicity in the "detention and diffusion" of images of a child-pornographic nature and the violation of a person's image rights with sexually explicit deepfakes, among other potential crimes.
Musk and former CEO Linda Yaccarino were summoned to a hearing on April 20.
Other X staff were also summoned as witnesses.
In July, Musk denied the initial accusations and said French prosecutors were launching a "politically-motivated criminal investigation".
"At this stage, the conduct of this investigation is part of a constructive approach, with the aim of ultimately ensuring that the X platform complies with French laws, insofar as it operates on national territory," the prosecutor's office said.
Such summons are mandatory, though they are harder to enforce on people who don't live in France.
After such a hearing, authorities can decide to either shelve or continue the probe, and potentially place suspects in custody.
Britain's Information Commissioner's Office, meanwhile, said it was investigating the xAI chatbot, following reports that Grok had been used to generate non-consensual sexual imagery of individuals, including children.
Britain's media regulator Ofcom said separately it was setting out the next steps in its investigation into X launched last month, though it provided few details.
Ofcom is seeking to assess if the company has done enough to mitigate the risk of sexual deepfakes spreading on its social media platform. But it has said it was not investigating xAI, which operates the Grok chatbot, as it falls beyond the scope of current law.
The European Union launched an investigation last week into X too, seeking to assess whether it disseminated illegal content, following a public outcry over the spreading of manipulated sexualised images by Grok.
The chatbot continues to generate sexualised images of people even when users explicitly warn that the subjects do not consent, Reuters has found.
xAI put some restrictions on Grok's image-generation function in response to the backlash last month.
The Paris prosecutor's cybercrime unit is conducting the investigation in France, together with the French police's own cybercrime unit and Europol.
