Federal transportation officials announced Tuesday that Japanese company Takata Corp. has agreed to recall roughly 34 million vehicles because of defective air bags, in the largest auto recall in U.S. history.

Takata agreed to the recall of the 33.8 million vehicles amid mounting pressure and fines from federal regulators over roughly the past year.

The air bag manufacturer was being fined $14,000 a day since late February, which now amounts to $1.2 million. The announcement was made Tuesday afternoon by the heads of the Department of Transportation and the National Highway Traffic Safety Administration, which reached an agreement with Takata. 

At issue is the chemical that inflates the air bags; it can explode with too much force, blowing apart a metal inflator and sending shrapnel into the passenger compartment. The faulty inflators are responsible for six deaths and more than 100 injuries worldwide. 

The move Tuesday will double the number of cars and trucks already recalled. 

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Eleven automakers -- including Honda Motor Co. and Toyota Motor Corp. -- have recalled 17 million vehicles in the U.S. and more than 36 million worldwide because of the problem. 

Those numbers will grow by millions because of the agreement, but it's unclear which manufacturers will be most affected by the expanded recalls.

Automakers must conduct recalls even if they are for defective parts. 

The Takata air bag recall dwarfs last year's highly publicized recall of 2.6 million General Motors small cars for defective ignition switches and Toyota's recalls of 10 million vehicles for problems with unintended acceleration. 

NHTSA Administrator Mark Rosekind said investigations by the agency and auto industry haven't determined precisely what's causing Takata's inflators to explode, but said the agency cannot wait for a cause to take action.

"We know that owners are worried about their safety and the safety of their families," he said. "This is probably the most complex consumer safety recall in U.S. history."

Rosekind also said people who get recall notices in the mail should immediately make an appointment to get their cars fixed.

The size of the recall compares to the 1982 recall of 31million bottles of Tylenol.

The Associated Press contributed to this report.