Mel to Oksana: Sue Me, I'll Sue You!

3/13/2011 3:59 PM PDT

Mel Gibson to Oksana Grigorieva -- Sue Me, I Dare You!

Mel Gibson will sue Oksana Grigorieva for extortion if she dares sue him ... this according to sources close to Gibson.

As TMZ first reported, Oksana still plans to file a lawsuit against Mel, alleging battery, emotional distress and defamation.

But sources close to Gibson tell us he will wage legal war if Oksana files -- and will NOT settle out of court. In fact, we're told Mel will gladly file his own lawsuit against the woman he says put a $15 million price tag on the tapes in return for keeping them secret.

Looks like this battle has just begun.