Britney Detained, "Evaluated" after Cops Make House Call (E! Online)

Los Angeles (E! Online) - When it rains, it pours.

Los Angeles police were called to Britney Spears gated Studio City, California, home Thursday night to resolve what authorities have deemed a custodial dispute involving her and Kevin Federlines two children, after which the troubled pop star was transported by ambulance to a nearby hospital.

LAPD spokesman Officer Jason Lee said that Spears was detained and taken in for evaluation after police arrived at her house and found her to be under the influence of an unknown substance.

Spears arrived at L.A.s Cedars-Sinai Medical Center just before 12:30 a.m., and is on medical hold, i.e. being detained, while docs of the physical and psychological variety check her out.

A second ambulance, reportedly containg a child, left Spears house shortly after the first one and was headed in the same direction.

Theres no immediate word on whether charges will be filed.

The cops were called at 8 p.m. and were still there at 10:30 p.m. when several other police cars, two ambulances, a firetruck, a police chopper and, of course, the press rolled up behind them.

A handful of paramedics were inside the house as of 11 p.m. and were said to be treating the 26-year-old singer, but no specific injuries have been reported.

Medics were seen rolling a gurney and other equipment into the house.

Lee couldnt say who originally called the police but did say the call was in reference to a family custodial dispute that we are trying to peacefully resolve. He later said that the children were turned over to Federlines camp at about 10:50 p.m., just as the medical cavalry was arriving, after police reviewed a court order stipulating that it was time for the toddlers father to be in charge.

K-Feds attorney, Mark Vincent Kaplan, was spotted arriving at the Spears home shortly before 8 p.m. this evening, but was seen leaving before the big to-do. Its unclear whether the court documents on hand were courtesy of Kaplan.

Us Weekly reported that the clash in question occurred when Federlines bodyguards arrived at Spears house this evening to retrieve two-year-old Sean Preston and year-old Jayden James, and Spears refused to hand over the boys.

In a normal case, when someone shows up with a certified court order saying the kids need to be somewhere else, the police see to it that the order is obeyed. But that is in a normal case, Spears soon-to-be former family attorney told Us. The Beverly Hills lawyer filed a motion Wednesday to have himself relieved as Spears counsel, citing a breakdown in communication.

The beleaguered songstress gets supervised visits with her sons three times a week under the terms of her current arrangement with Federline. She lost custody to her ex in October after defying a judges order not to drive the boys around without a valid license and insurance.

Also per court order, Spears is supposed to log several hours a week with a parenting coach and undergo twice-weekly random drug testing, a provision her lawyers have fought, but to no avail.

Earlier Thursday, Spears was about 90 minutes late for her appointment to be deposed by Federlines legal camp. Thanks to her tardiness, Kaplan was only able to question the Toxic singer for 14 minutes.

(Originally published Jan. 3, 2008 at 10:28 p.m. PT)