TMZ.com said Spears' visitation rights have been "suspended pending further order of the court."

Federline was last year awarded temporary physical custody of Jayden James, 1, and Sean Preston, 2, while Spears was granted limited, supervised visits with the boys.

Spears was undergoing a 72-hour mental evaluation at a Los Angeles hospital Friday after refusing to give Jayden back to her ex-husband at the end of a visit Thursday evening.

People.com quoted a source who said Spears' court-appointed child monitor called police after the troubled pop star locked herself in a room with Jayden and refused to turn him over to an assistant to Federline.

"(The monitor) had already put Preston in the car when Britney locked herself in a room with Jayden," the source said. "The cops came and got through the door and tied her down to a gurney."

Police said Spears appeared to be "under the influence of an unknown substance" at the time of the incident.

They also determined the children were supposed to be with Federline.

Spears was taken by ambulance to Cedars-Sinai Medical Center where the source told People.com the singer will be on a minimum of a 72-hour lock-down for mental evaluation.

Preston was taken to the hospital by Federline's assistant, while Jayden was transported with the monitor by ambulance.

The children reportedly were not treated for any injuries and Federline took the boys home early Friday morning.