JSON and XSS_clean method

[eluser]Unknown[/eluser]
Hello

I receive in a POST request a JSON encoded string.
My question is simple: Can I use xss_clean() on the encoded JSON string? or do I first have to decode it and execute the xss_clean() on each field in my object?
Can the method xss_clean() "break" a well-formed JSON encoded string?

Thank you,