Updated at 3:13 p.m. ET

Japanese air bag supplier Takata says nearly 34 million vehicles were fitted with its defective inflator mechanisms, doubling the number of vehicles affected in the U.S., the National Highway Traffic Safety Administration said Tuesday.

The recall is believed to be the largest in NHTSA's history.

Under an agreement, NHTSA issued what's called a consent order to Takata that requires the company to cooperate fully with the agency's investigation. NHTSA also announced that it will begin a formal legal process "to organize and prioritize the replacement of defective Takata inflators under the agency's legal authority."

"Today is a major step forward for public safety," Transportation Secretary Anthony Foxx said. "The Department of Transportation is taking the proactive steps necessary to ensure that defective inflators are replaced with safe ones as quickly as possible, and that the highest risks are addressed first. We will not stop our work until every air bag is replaced."

Here's more from the department's statement:

"The actions expand regional recalls of Takata passenger-side inflators, currently limited to areas of high absolute humidity, to nationwide recalls involving more than 16 million vehicles. They also expand the current nationwide recall of driver-side inflators to more than 17 million vehicles."

The problem lies with Takata air bags that can potentially explode, sending metal shards flying into the passenger compartment. The air bags have been linked to six deaths and more than 100 injuries worldwide, prompting lawsuits and a criminal inquiry in the U.S. It's unclear what causes the inflators to malfunction.

A NHTSA statement said "these inflators were made with a propellant that can degrade over time and has led to ruptures."

Ten automakers are affected and NHTSA said it was waiting for them to supply a complete list of affected vehicles. Honda, Toyota and eight other automakers have already recalled 17 million vehicles in the U.S. and more than 36 million worldwide in connection with the problem. Those numbers will now increase.

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