Federal regulators have approved a General Motors Co. proposal to revise the structure of its Chevrolet Volt to reduce the risk of an electrical fire.

The redesign was prompted by a "formal safety defect investigation" by the National Highway Traffic Safety Administration into the Volt's lithium-ion battery pack, after two fires that followed crash tests, Wired.com reported Thursday.

GM has defended the Volt, which has received a five-star safety rating, but said the modifications will make the car safer.

"The Volt has always been safe to drive. Now, we will go the extra mile to ensure our customers' peace of mind in the days and weeks following a severe crash," Mary Barra, senior vice president of global product development, said.

In June a Volt caught fire three weeks after a side-impact crash that punctured the battery pack and caused coolant to leak, eventually causing a short circuit, GM said.

GM said it would strengthen part of the Volt's underbody to increase protection of the pack in a severe side collision.