(Reuters) -The U.S. National Highway Traffic Safety Administration said on Wednesday it had opened a preliminary evaluation into 17,198 Rivian electric delivery vans over seat belt concerns.

The probe focuses on the driver's front outboard seat belt anchorage system, which uses a steel-braided cable to secure the belt to the seat frame.

According to the NHTSA's Office of Defects Investigation (ODI), six complaints from vehicle owners described cables that frayed, broke, or unravelled, leaving drivers at risk of being unrestrained in a crash or sudden stop.

Rivian did not immediately respond to a request for comment. 

Regulators said there have been no reported crashes, fires, injuries, or fatalities linked to the potential defect. The NHTSA warned that a weakened or detached seat belt anchorage could fail to meet required load capacity standards, creating what it called "an unreasonable risk to motor vehicle safety."

Investigators will now examine the integrity of the seat belt assembly, the installation method, and whether any design or manufacturing deficiencies contributed to the issue.

The preliminary evaluation is the first step in the NHTSA's defect process. It could lead to an engineering analysis and, if warranted, a recall.

(Reporting by Akash Sriram in Bengaluru; Editing by Anil D'Silva)