PARIS, April 21 -- ​Tech billionaire Elon Musk on Monday did not appear at a summons for questioning in a French probe into X and its AI chatbot, Grok, over alleged abuse of algorithms and fraudulent data ‌extraction, the Paris prosecutor's office said.

The investigation, which has been expanded in past months to include suspected complicity in ​the distribution of child pornography and the creation of sexual deepfakes by Grok, has added to strains in relations between the US and Europe over Big Tech and free speech.

The April 20 summons date was set in February, when the Paris prosecutor's cybercrime unit raided the French office of ​Musk's social-media platform, X.

"The prosecutor's office notes the absence of...