WASHINGTON -- A minor who was driving a car that crashed near Pittsburgh has been tentatively identified by the government as the eighth death in the U.S. due to an explosive air bag inflator made by auto parts maker Takata, federal transportation officials said Wednesday.

The National Highway Traffic Safety Administration officials also announced an expansion in the recall of vehicles with Takata airbags, already the largest and most complex recall in the agency's history. The latest findings could result in the recall of several hundred thousand additional vehicles, officials said.

The appointment of an independent monitor to oversee the company's compliance with a government consent order on the recalls was also announced.

NHTSA learned of the latest death last week after a lawyer for the minor's family contacted the agency, NHTSA spokesman Gordon Trowbridge told reporters in a conference call. The car involved was a used 2001 Honda Accord under recall that was owned by a relative of the minor, he said. But a government official told The Associated Press that a boy was driving the car when it left the road and struck a tree. The official provided the information on condition of anonymity because he wasn't authorized to speak publicly.

"The agency has now tentatively concluded that this was likely a rupture-related fatality," Trowbridge said. The agency is now working the family, Takata and Honda to examine the vehicle in order to confirm that conclusion, he said.

A woman in Malaysia was also killed by a rupturing Takata air bag last year, the only known fatality outside the U.S., bringing the global number of deaths to nine. More than 100 other people have been injured by the Takata inflators, which can explode with too much force, sending shrapnel into drivers and passengers.

In the U.S., about 23 million Takata air bag inflators have been recalled on 19 million vehicles sold by 12 auto and truck makers. Many of the air bag deaths and injuries involved low-speed crashes that otherwise would likely have been survivable, Trowbridge said.

Recent crash testing of vehicles already among those recalled resulted in five passenger side air bag inflator ruptures, he said. As a result, NHTSA is expanding the number of recalled vehicles to include other model years of the five vehicles involved in the tests as a safety precaution, he said. All the vehicles involved in the tests had spent substantial time in high humidity regions, he said.

Takata uses ammonium nitrate to create a small explosion that inflates the air bags in a crash. But the chemical can deteriorate under prolonged exposure to airborne moisture, causing it to burn too fast and blow apart a metal canister designed to contain the explosion.

While he didn't have a specific number for the vehicles being added to the recall, Trowbridge said it would likely amount to several hundred thousand vehicles.

"We have a great big problem here and it's going to take a long time to get it fixed," Trowbridge said.

The vehicles being added to the recall are Mazda 6 model years 2005 to 2008, Honda CRV model years 2002 to 2004, Subaru Legacy model years 2005 to 2008 and Subaru Outback model years 2005 to 2008. The expanded Honda recalls alone involved 127,000 inflators in vehicles not previously recalled, the carmaker said.

Honda urged owners of the recalled cars to get their vehicles repaired at their local dealer as soon as possible. "Honda has sufficient replacement parts supplies to begin recall repairs of the added vehicles immediately, nationwide," the company said in a statement.

Eventually, all airbag inflaters that use ammonium nitrate are expected to be recalled, Trowbridge said. Takata is the world's largest air bag maker, and that would potentially add tens of millions of inflators to the recall rolls.

The good news, Trowbridge said, is that the pace of repairs of vehicles with faulty inflators has picked up significantly. As of Dec. 4, more than 27 per cent of recalled driver's side airbag's and nearly 26 per cent of recalled passenger side air bags had been repaired, he said.

NHTSA also announced the appointment of John Buretta, a former principal deputy assistant attorney general in the Justice Department's criminal division, to oversee Takata's compliance with an air bag recall compliance agreement with the government. Buretta is a partner of the law firm Cravath, Swaine & Moore.

The agency has fined Takata $70 million for delays in disclosing the safety defect, and warned that the company could face an additional $130 million penalty if it doesn't fulfil the terms of the consent order.