May 10 (Reuters) - The U.S. auto safety regulator said on Friday it was opening a preliminary evaluation into 210,960 Ford vehicles following complaints alleging diesel fuel leaks that may result in a fire.

The National Highway Traffic Safety Administration said it has received 27 complaints, including 12 reports of fires and a total of four injuries, and that it would investigate Ford F-250, 350, 450, and 550 Super Duty vehicles equipped with 6.7L diesel engines of model years 2015-2021.

The agency's preliminary evaluation is the first step to determine whether the vehicles pose an unreasonable risk to safety. It could close the investigation without taking any potential action.

The NHTSA said a fracture in the secondary fuel filter in the vehicles could result in a fire, as the proximity of the filter to high heat sources creates a potential for auto-ignition thermal events and fires.

Ford was not immediately available for a comment.

(Reporting by Deborah Sophia in Bengaluru; Editing by Krishna Chandra Eluri)