U.S. safety regulators said they had closed an investigation into electric sports car maker Tesla Motors Inc.'s popular Model S sedans.

The U.S. National Highway Traffic Safety Administration began investigations into the company's Model S luxury electric cars in November after three cars caught fire.

"A defect trend has not been identified," the regulator said on its website. "The closing of the investigation does not constitute a finding by NHTSA that a safety-related defect does not exist."