General Motors is recalling about 619,000 small cars in the U.S. because either a heavy key ring or a "jarring event" such as running off the road could cause the ignition to shut off and possibly prevent the air bags from deploying in a crash, the automaker said in a report posted Thursday on the National Highway Traffic Safety Administration’s website. The vehicles affected by the recall are the 2007 Pontiac G5 and the 2005-07 Chevrolet Cobalt.

In addition to the vehicles being recalled in the U.S., 153,000 in Canada and 6,100 in Mexico are being recalled.

In a separate news release, GM said it knew of six deaths in five crashes in which the front air bags did not deploy.

"All of these crashes occurred off-road and at high speeds, where the probability of serious or fatal injuries was high regardless of air bag deployment. In addition, failure to wear seatbelts and alcohol use were factors in some of these cases," the statement said.

Alcohol was involved in two of the five crashes, resulting in three of the deaths, Alan Adler, a spokesman for GM, said in a telephone interview. The statement said GM was also aware of 17 other crashes "involving some type of frontal impact and nonfatal injuries where the air bags did not deploy."

Adler said that it was possible that hitting a deep pothole could turn off the ignition, but that GM had received no such reports. A figure for the weight of key rings causing the problems was not available.

The automaker told the federal agency that the "ignition switch torque performance may not meet General Motors’ specification" on the vehicles, which were assembled in Lordstown, Ohio.