Police Investigating Mel Gibson's Extortion Claims Against Oksana

By Eunice Oh

07/21/2010 at 04:15 PM EDT

In yet another chapter of Mel Gibson and Oksana Grigorieva's bitter break-up, authorities are investigating whether or not the actor's ex-girlfriend tried to extort money from him.

"Extortion allegations were brought to our attention [and] we're looking into it," L.A. Sheriff's spokesman Steve Whitmore tells PEOPLE.

Gibson, 54, previously claimed the Russian musician, 40, demanded cash from him and, if he didn't pay, threatened to leak recordings of him spewing racist comments and threatening her to the media.

RELATED: Mel & Oksana: Why Their Custody Battle Went Nuclear

A source says Gibson was planning to present evidence to detectives proving Grigorieva broke the law. He also asserted that she made false claims to police about his alleged abuse.

According to Grigorieva's rep, police aren't launching a full investigation, however. "Looking into something is very different than launching a formal investigation," Grigorieva’s spokesperson Stephen Jaffe, told PEOPLE.

• Reporting by OLIVER JONES and KEN LEE

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