WASHINGTON (Reuters) - The U.S. National Highway Traffic Safety Administration said on Friday it was rejecting a petition by Ford Motor Co F.N to delay recalling about 3 million vehicles with potentially defective air bag inflators to conduct additional testing.

The logo of Ford is seen during the 87th International Motor Show at Palexpo in Geneva, Switzerland March 8, 2017. REUTERS/Arnd Wiegmann

The agency said it did not find the request by the second largest U.S. automaker “reasonable under the circumstances or supported by the testing and data it has collected to date.”

Takata inflators can explode with excessive force, unleashing metal shrapnel inside cars and trucks. At least 18 deaths and 180 injuries worldwide have been tied to the defect that led Takata Corp TKTDQ.PK to file for bankruptcy protection in June and prompted at least 19 automakers to issue recalls.

NHTSA also rejected a similar petition filed by Mazda Motor Co 7261.T covering about 6,000 vehicles. Mazda said in a statement it "takes our customers' safety as a single-minded top priority and continues to work hand-in-hand with NHTSA."

The public can comment on NHTSA’s decision until Dec. 18 on both Ford and Mazda’s petitions. Mazda said it would “provide further information once NHTSA issues its final determination.”

Ford did not immediately say if it planned to challenge the agency’s decision. “We will cooperate with the agency, as we always do,” spokeswoman Elizabeth Weigandt said in an email. The vehicles in question include the 2007-11 Ford Ranger, 2006-12 Fusion and Lincoln MKZ, 2006-11 Mercury Milan, and 2007-10 Ford Edge and Lincoln MKX.

In July, NHTSA said new testing prompted Takata to declare inflators defective in Ford, Nissan Motor Co 7201.T and Mazda vehicles in some driver-side air bags. Nissan agreed to a recall of 515,000 vehicles.

NHTSA agreed in 2016 to a request by General Motors Co GM.N to delay a recall of 2.5 million vehicles with Takata air bag inflators as the Detroit automaker conducts additional testing to determine if the vehicles need replacement inflators.

Separately, a report issued on Friday by an independent monitor of the Takata recalls said more than 10 million U.S. vehicles and 18.5 million faulty Takata air bag inflators remain unrepaired in the largest ever auto recall.

Takata has said it expects to have recalled 125 million vehicles worldwide by 2019.

The report said 43.1 million Takata airbag inflators were under recall in 31.5 million vehicles today, with scheduled expansion to about 65 million inflators by the end of 2018. Of those, 24.6 million inflators in 20 million vehicles have been repaired.

In 2019, another 4.1 million vehicles will be recalled to replace interim inflators.