FBI Investigating Brad Pitt for Alleged Child Abuse: Source

— -- The FBI is now investigating Brad Pitt over an allegation of child abuse, a source told ABC News.

The news of FBI involvement comes after sources told ABC News that the actor was being investigated by the Los Angeles Department of Children and Family Services.

An alleged incident aboard a flight from France to Minnesota to Los Angeles prompted the FBI's involvement in the investigation, the source said. The federal agency was notified Monday of the allegation, and agents were instructed to perform an assessment, the source said. Agents are also trying to determine which child or children were involved and if the alleged incident was physical or just verbal.

The source added that based on preliminary information there is no suspicion of drug use being involved in the alleged incident.

If any charges in relation to the allegation were to be filed against Pitt, a source told ABC News that they'd likely be misdemeanors.

Sources close to Pitt told ABC News that the actor is taking the allegations very seriously and cooperating with authorities. However, they added, many of the claims made against him are either exaggerated or outright fabricated.

News of the investigation comes just days after Angelina Jolie Pitt filed for divorce from the actor, a decision her attorney said earlier this week was "made for the health of the family."

Pitt, 52, and Jolie Pitt, 41, were married for two years before their split. In the divorce document obtained by ABC News, the estranged couple's date of separation was listed as Sept. 15. Jolie Pitt has asked for physical custody of the couple's six children, Maddox, 15, Pax, 12, Zahara, 11, Shiloh, 10, and twins Knox and Vivienne, 8.

"I am very saddened by this, but what matters most now is the well-being of our kids," Pitt said earlier this week.

The actor has not yet responded to the abuse allegation, though sources told ABC News that his number one priority remains the welfare of the children.