TOM KRISHER, AP Auto Writer

DETROIT (AP) — U.S. safety regulators are threatening fines and legal action against Takata Corp. for failing to admit that its driver’s-side air bag inflators are defective and should be recalled nationwide.

The National Highway Traffic Safety Administration sent a letter to the company Wednesday detailing the threats, which include a public hearing and possible court action.

Takata of Japan has refused demands for the national recall, saying that a recall limited to high-humidity states is sufficient. But the agency says two inflators have ruptured in cars outside the high-humidity zone, injuring drivers by spewing metal fragments.

Transportation Secretary Anthony Foxx says Takata must act quickly or the agency will use all of its authority and resources to get the national recall done.