DETROIT (Reuters) -- U.S. auto safety officials on Friday told Takata Corp. to work harder to meet demand for replacement parts for airbags that could prove defective in millions of U.S. cars.
On Thursday, Takata agreed to add two production lines to make more air bag parts. The pledge came at a meeting with the National Highway Traffic Safety Administration, which said on Friday that the effort might not be enough.
"It's unclear yet whether that would be sufficient to meet demand," said NHTSA Deputy Administrator David Friedman in a statement released Friday evening.
Friedman also said Takata had not yet heeded NHTSA's request to contact other airbag suppliers to help speed up production of replacement parts for Takata airbags "due to concern for quality issues."
A Takata spokesman did not respond immediately to a request for comment on Friday. On Thursday, Takata spokesman Alby Berman said the company "is cooperating fully with NHTSA and is working to meet their requests."
Friedman said NHTSA was "reaching out to other suppliers and manufacturers to discuss the potential and risks of having those suppliers provide replacement airbags" on more than 4 million U.S. cars that have been recalled since June.
NHTSA on Thursday ordered Takata to provide documents and answer questions under oath related to the government's ongoing probe of the company's airbags and inflators, which can explode with excessive force and spray metal shards into vehicle occupants.
Since 2008, 10 global vehicle manufacturers that use Takata airbags have recalled more than 10 million cars in the United States and more than 17 million worldwide to replace inflators that have been linked to at least four deaths and numerous serious injuries.
The list continues to grow.
On Friday, NHTSA posted documents covering the recall of 1,848 Infiniti SUVs made by Nissan Motor Corp. The 2013 QX56 and 2014 QX80 SUVs are being recalled in the United States as part of a larger global recall announced on Oct. 23.
The issue, which has also affected vehicles built by General Motors and Honda Motor Co., is the installation by Takata of an incorrect part in the airbag inflator that can cause the driver side airbag to rupture.
In June, NHTSA launched its probe of whether Takata airbag inflators made from 2000 to 2007 were properly sealed or subject to other defects. It also asked the automakers to recall airbags in certain regions, such as Florida and Puerto Rico, where the parts were exposed to higher moisture and humidity that could cause deterioration of the explosive material inside.
Critics have said Takata and NHTSA have not moved fast enough on the issue.
On Thursday, lawyers for U.S. consumers asked a federal judge in Miami to speed up a class action against Takata and four automakers, saying public safety was at stake.