UPDATE 1-US regulators investigate Kia Soul steering loss

* Complaint of steering loss in a 2-month-old Kia Soul

* Safety regulators eye more than 51,000 vehicles

* Complaint said incident happened 'without warning' (Adds Kia comment)

DETROIT, Aug 17 (Reuters) - U.S. safety regulators have opened a preliminary investigation into a potential problem with the Kia Soul after a driver reported a complete loss of steering and limited braking in a two-month-old car.

The National Highway Traffic Safety Administration said the issue could affect more than 51,000 Kia Soul vehicles.

NHTSA received one complaint from an owner of a nearly new Kia Soul who said the steering shaft detached from the steering wheel and then fell onto the driver's side floor in a way that interfered with the brake pedal.

NHTSA said its Office of Defect Investigation was "very concerned" the reported failure had happened "without warning" and in a two-month-old car after 4,300 miles of driving.

"It occurred without warning on a new vehicle at low mileage and resulted in a complete loss of steering as well as a compromised brake system," safety regulators said in a statement released on Monday.

Kia said in a statement that it was cooperating with NHTSA and working with its suppliers to determine if there was a problem in its manufacturing.

Kia is "committed to sharing information and findings with NHTSA's (Office of Defects Investigation) on an ongoing basis in order to reach a prompt resolution," the company said.

Kia is an affiliate of Hyundai Motor Co (005380.KS). A Kia representative could not be reached immediately for comment.

The Korean automaker had sold over 36,000 of the cube-shaped Soul models as of the end of July.

The early success of the Soul, which has been marketed to the same younger drivers targeted by Toyota Motor Corp's (7203.T) Scion brand, has helped push Kia sales higher for the year.

Through July, Kia's U.S. sales were up 16.3 percent, outperforming the 14.3 percent rise in overall industry sales, according to Autodata Corp. (Reporting by Kevin Krolicki; Editing by Derek Caney and Gunna Dickson)