LOS ANGELES — Mel Gibson is being investigated in a possible domestic violence incident involving his ex-girlfriend earlier this year, sheriff's officials said Thursday.

The Los Angeles County Sheriff's Department listed the actor-director as a potential suspect in the alleged attack on Russian singer Oksana Grigorieva at an undisclosed location in Malibu.

The two have been involved in a nasty custody dispute over their infant daughter -- the subject of a confidential court case.

The incident is being investigated by the same sheriff's substation that handled Gibson's 2006 arrest on suspicion of drunken driving. The station in Agoura also covers Malibu, where Gibson lives.

The release states the incident occurred Jan. 6 and the investigation is in a preliminary stage. A department spokesman was not immediately available to speak about the case.

A phone message left for Alan Neirob, Gibson's spokesman, was not immediately returned.

The Academy Award winner is no longer on probation for the drunken driving case and his conviction has been expunged.

The actor has not publicly discussed the breakup with Grigorieva, 40. The former couple first revealed their relationship shortly after Gibson's wife, Robyn, filed for divorce last April.