U.S. safety officials said Friday they are opening an investigation concerning the safety of Chevy Volts after another Volt caught fire in a test a week ago.

The National Highway Traffic Safety Administration (NHTSA) said in a statement today it is concerned that damage to the Volt's lithium batteries -as part of three tests that are explicitly designed to replicate real-world crash scenarios- have resulted in fire.

"While it is too soon to tell whether the investigation will lead to a recall of any vehicles or parts, if NHTSA identifies an unreasonable risk to safety, the agency will take immediate action to notify consumers," it said in a statement Friday.

The agency conducted three tests last week on the Volt's lithium-ion battery packs that intentionally damaged the battery and ruptured the coolant line.

One of the batteries which was rotated began to smoke and emit sparks during testing. A second battery pack caught fire at the testing facility on Thursday.

In May the NHTSA conducted a test where a Volt was crashed and its battery was damaged. Three weeks later, the car caught fire.

The NHTSA concluded that the damage to the vehicle's lithium-ion battery during the crash test led to the fire, according to a Friday statement.

The agency said General Motors and other government agencies are cooperating in the investigation. See the statement here.