The U.S. auto safety regulator on Tuesday called on Japanese supplier Takata and five automakers to expand nationwide a regional recall of potentially deadly air bags, increasing pressure on the industry to act more swiftly in the growing scandal.

The National Highway Traffic Safety Administration also scolded Takata for what it called "an unwillingness to move forward" on a nationwide recall and said Takata needed to be frank with the American public about the risks of its air bags.

Auto safety advocates and lawmakers immediately criticized NHTSA's latest move. They said it still may not capture the scope of the problem, is coming too late and is not an enforceable mandate.

A representative from Takata did not immediately respond to a request for comment.

Takata and automakers so far have taken a targeted approach in recalling U.S. vehicles with air bags that can potentially rupture upon deployment, shooting metal shards inside the car. Five fatalities, including four in the United States, have been linked to the air bags.

The U.S. regional recall involved 4.1 million cars in hot and humid areas where the air bags could be prone to fail, including Florida, Alabama, Mississippi, Georgia, Louisiana and parts of Texas along the Gulf of Mexico.

NHTSA Deputy Administrator David Friedman told reporters on Tuesday that the call to expand the recall was prompted by an August incident involving a 2007 Ford Mustang in North Carolina, outside the area previously included in the regional recall of the air bags.

The agency ordered Ford Motor Company, Mazda Motor Co., Honda Motor Co., Chrysler Group LLC and BMW to send notifications for replacement driver's-side air bags to consumers quickly.

"We will begin a process both with Takata and the automakers to force them to recall all affected" vehicles, Friedman said.

Over the past six years, roughly 16 million cars with Takata air bags have been recalled worldwide. That includes more than 10 million in the United States, of which the regional recall is a part.

Friedman declined to estimate how many more cars would be included in the nationwide recall of driver's side air bags.

It is also unclear whether there are enough parts available to cover the expansion in a timely manner. NHTSA said it is pressuring Takata to ramp up production of replacement parts and has said it will explore using other suppliers to help with production if needed.

Ford, Honda, Mazda and Chrysler all said they would continue to cooperate with NHTSA and plan to evaluate their call for a national recall. But each stopped short of saying they would expand beyond the current set of cars they are repairing. BMW is already recalling air bags nationally.

NOT ENOUGH

Democratic Senators Ed Markey and Richard Blumenthal said they were pleased NHTSA had recognized the "national scope of this problem" but said Tuesday's call to replace driver's-side air bags should be expanded to include passenger air bags.

They also said the agency should revisit the policy that allows recalls to be regional rather than national.

NHTSA agreed in June to allow automakers to do a regional recall and use their discretion in deciding how and when to notify customers and replace the faulty parts, resulting in confusion for car owners receiving mixed messages.

Safety advocate Clarence Ditlow, executive director of the Center for Auto Safety, said NHTSA's action on Tuesday is coming too late. "They never should have accepted in June of 2014 anything less than a national recall," Ditlow said.

TIME TO BE FRANK

Friedman on Tuesday also directed harsh criticism at Takata, saying the company was resistant when NHTSA this week called on it to issue a defect notification nationwide for air bags of a certain design.

"Takata's initial response was an unwillingness to move forward, and frankly, that is one of the reasons that we are talking to all of you today, because I believe that everyone needs to understand that Takata needs to act," Friedman said.

The regulator also addressed lingering confusion over what exactly makes some air bags explode.

NHTSA said on Tuesday it had ordered Takata to provide under oath documents and other information on the propellant used in newly designed air bag inflators, after Takata recently said it had changed the chemical mix of its inflators.

The regulator also said it needed more information on the steps Takata and automakers are taking to "control and mitigate" the risks associated with the defective inflators.

"The agency is demanding this information to compel Takata and the affected industry to be frank with not only NHTSA, but the American public," NHTSA said in a statement.