DETROIT — The U.S. government's highway safety agency has decided to open two new investigations into fires involving Hyundai and Kia vehicles after getting complaints of more than 3,100 fires and 103 injuries.

The National Highway Traffic Safety Administration said Monday that it granted a petition filed last June seeking the investigations by the nonprofit Center for Auto Safety, a consumer advocacy group.

The investigations, one for Hyundai and the other for Kia, cover noncrash fires in almost 3 million vehicles from the affiliated Korean automakers. The probes cover the 2011 through 2014 Hyundai Sonata and Santa Fe, the 2011 through 2014 Kia Optima and Sorento, and the 2010 through 2015 Kia Soul. The complaints came from consumers and from data provided by both automakers.

One death was reported involving a Kia vehicle, according to the documents.

NHTSA had previously said it would incorporate the noncrash fires into a 2017 investigation that examined recalls of Hyundai and Kia vehicles for engine failures. It opened the new probes "based on the agency's analysis of information received from multiple manufacturers, consumer complaints and other sources."

Jason Levine, executive director of the center, said in a statement that it is long past time for the agency to investigate why so many Kia and Hyundai vehicles have caught fire when not involved in crashes.

"While it may be six months post-due, we are gratified to see NHTSA's Office of Defect Investigations open formal investigations based on our petition," Levine said.

The center contended that there are more noncrash fires in the Hyundai and Kia cars and SUVs than in similar vehicles made by other automakers.

Hyundai and Kia said in statements that they're cooperating with the investigations and have been open and transparent with NHTSA, providing comprehensive data. Messages were left seeking comment from NHTSA.

In documents detailing the investigations, NHTSA reported that it had received complaints of engine compartment fires, as well as fires involving other components including tail light housings, wiring harnesses, and light bulbs. Agency investigators sent information requests to both automakers in September and October of last year, according to the documents.

The investigation will look into how often fires happen, how many vehicles are affected and the safety-related consequences, the documents said.

Engine failure and fire problems with Hyundais and Kias have affected more than 6 million vehicles since 2015, according to NHTSA documents. So far, Hyundai and Kia have recalled about 2.4 million vehicles to fix problems that can cause fires and engine failures.

In addition, the automakers are doing a "product improvement campaign" covering another 3.7 million vehicles to install software that will alert drivers of possible engine failures and send the cars into a reduced-speed "limp" mode if problems are detected.

Just last Friday, NHTSA announced a recall of about 20,000 Veloster cars with 1.6-liter engines in the U.S. and Canada because fuel can prematurely ignite in the cylinders around the pistons. That can cause excessive pressure and damage the engine, causing vehicles to stall and in some cases catch fire.

But that's a different problem from what has caused the rest of the recalls since 2015.

In February, Kia announced that it would recall the Soul small SUV with the same-size engine due to engine failure and fire problems, but for reasons unrelated to the Veloster's issues.