June 13 (Reuters) - The European Commission has asked internet platforms Pornhub, Xvideos and Stripchat what measures they take to protect minors and to prevent the spread of illegal content online.

The companies must provide detailed information on measures they have taken to assess and mitigate risks for minors online and to prevent amplification of illegal content and gender-based violence by July 4, the Commission said on Thursday.

Among other information, the Commission requires "details on age assurance mechanisms adopted by these pornographic platforms", it said.

The European Union last year added the three adult content companies to its list of companies subject to stringent regulations under new online content rules.

The rules under the Digital Services Act (DSA) require companies to share data with authorities and researchers, conduct risk management and undergo external and independent auditing.

They also allow the Commission to impose fines for incorrect, incomplete or misleading information in response to a request for information. (Reporting by Bart Meijer Editing by Benoit Van Overstraeten and David Goodman )