The National Highway Traffic Safety Administration said it is investigating reports of engine compartment fires in certain BMW Mini vehicles. The investigation includes about 36,000 Mini Cooper S, Cooper S Clubman and Cooper S convertibles from the 2007 and 2008 model years.

According to the agency, its Office of Defects Investigation, which probes such allegations, has received 12 complaints of engine compartment fires in Cooper S vehicles, including 5 reports of fires that enveloped and destroyed the vehicles. In eight cases, complainants allege the fires occurred while the vehicles were parked with the ignition off.

The agency said it received most of the complaints in the last year, indicating an increasing trend. NHTSA said opened what it officially calls a preliminary evaluation “to assess the cause, scope and frequency of the alleged defect.” Such investigations sometimes lead to safety recalls.

A Mini spokeswoman said the car maker is working with NHTSA to determine the cause of the fires.