Japan's Mazda Motor Corp will broaden a recall of cars sold in the United States because an air-bag inflator, supplied by Japan's Takata Corp, could rupture and seriously injure occupants, reported Reuters.

The issue of ruptured inflators - which can hurl metal shrapnel at vehicle occupants - has bedeviled Takata and triggered the recall of millions of vehicles last year. The company supplied the parts to at least nine global automakers.

The recalls were expanded this year as issues cropped up in newer models equipped with Takata air bags and inflators.

In a filing Friday by the U.S. National Highway Traffic Safety Administration, Mazda said it would recall about 18,000 older models, including 18,000 Mazda6 sedans and 50 RX-8 sports cars from 2003-2004.

NHTSA said the inflator could rupture, "with metal fragments striking and potentially seriously injuring" occupants.

The U.S. recall is part of a global recall of nearly 160,000 vehicles for similar issues announced by Mazda on June 23.

Indeed, over the past five years, about 12 million vehicles equipped with Takata air bags have been recalled around the world for similar issues.

Last week, German automaker BMW said it would recall another 1.6 million cars with Takata air bags because of the risk of injury from inflators that could rupture.

In two separate actions Friday, NHTSA said it had opened investigations into cars made by Hyundai Motor Co and Chrysler Group.

NHTSA said it was investigating nearly 400,000 2006-2006 Hyundai Sonata sedans after receiving complaints that the seat belt buckle assembly had failed. The safety agency said the problem could cause air bags to fail in a crash.

It was also investigating about 123,000 2011-2012 Dodge Chargers over complaints about engines stalling and alternator failure.