Mel Gibson allegedly threatened to bury his ex-girlfriend in a "rose garden".

The 'Mad Max' actor apparently makes the threat to OKSANA GRIGORIEVA during an argument which she recorded on tape for her own safety.

An insider told "Mel made a series of serious and violent threats against Oksana.

"When things in their relationship started going badly and he made the first threats against her, Oksana decided she needed to protect herself.

"She made the recordings and on one of them, Mel is heard telling Oksana, 'I will bury you in the rose garden,' which she believed to be a clear reference to killing her."

The alleged threat is contained on audio footage which has been handed over to the Los Angeles County Sheriff's Department to aid them in their "spousal abuse" investigation into Mel and Oksana's relationship.

Officers are also specifically looking into a violent altercation which is said to have taken place on January 6 and which left Oksana with broken teeth and concussion.

The Russian singer - who is fighting the 54-year-old Hollywood star for custody of their eight-month-old daughter Lucia - was interviewed by deputies on Monday (05.07.10).

She is believed to have told officers she was the victim of violence on several occasions and made the decision to secretly tape Mel's behaviour when it got really bad for her own protection.