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Did Oksana Grigorieva try to extort Mel Gibson?

That's what sources tell, which reports that the Russian singer, 40 -- with whom Gibson, 54, is in an ugly custody dispute over their 8 1/2-month-old daughter -- demanded more than $10 million to keep his infamous profanity-laced recorded rants a secret.

According to TMZ, Gibson's lawyers plan to meet with L.A. County Sheriff's deputies to present physical evidence of the alleged extortion scheme in hopes that detectives launch a formal investigation.

Grigorieva's rep tells Entertainment Tonight that the singer did not release the audio tapes -- five of which have been posted on RadarOnline and paint Gibson as a racist, violent man.

The rep also says claims that the tapes were edited to cast Gibson in a bad light are "ridiculous."

At a closed hearing Thursday morning (attended by several sheriff's investigators and lawyers for Gibson and Grigorieva ), detectives received the recordings.

They are examining the authenticity of the tapes, Sheriff's spokesman Steve Whitmore told the Associated Press.

Detectives are currently investigating whether Gibson abused Grigorieva (she claims he roughed her up in January).

Still no word whether the case will be turned over to prosecutors, who will decide whether Gibson should face criminal charges.