Italian automaker Pagani was to begin selling its $1 million, 700 horsepower Huayra supercar in the U.S. later this year but federal safety regulators have said "Not so fast."

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Pagani had applied for an exemption from federal auto safety rules requiring child-safe "advanced" airbags, arguing that complying with the rule would have caused "substantial economic hardship," according to documents from the National Highway Traffic Safety Administration.

NHTSA denied the request, essentially blocking the car from sale in the U.S., because Pagani failed to show that installing the airbags on the twin-turbocharged 12-cylinder carbon-titanium car would cause the company undue financial strain. Also, the Italian carmaker didn't show that serious efforts had been made to comply, the agency said.

The auto safety agency sometimes grants temporary exemptions from specific safety rules, especially for automakers that plan to sell only a small number of cars.

Pagani created the Huayra as part of the automaker's plan to break into the U.S. market. The car was engineered and crash tested to meet safety standards in both the U.S. and Europe.

Pagani insists it will sell the car here, just not in 2012 as it had planned. The Huayra will now go on sale some time in 2013, Paganai spokeswoman Sanaz Bakhtiari said.

Advanced airbags are designed to sense when children or small adults are in the vehicle and adjust the force with which they deploy accordingly. Early airbags were found to injure -- and even kill -- small children.

Much of the Huayra's structure, particularly the area around the driver, is made from a strong, lightweight material called carbon-titanium. The fuel tank, made from "different composite and ballistic materials," is integrated into the body just behind the cabin, according to the company.

At about 3,000 pounds, Pagani boasts that the Huayra is the lightest car in its class, enabling it to go from a zero to 60 miles per hour in about 3.5 seconds.

With it's seven figure price tag the Huayra would have competed in the rarified pricing sphere of cars like the Bugatti Veyron which is finishing its sales run just as just the Huayra was preparing to enter the market, or the quickly sold out Lamborghini Reventon.

With a total of only 60 employees, Pagani's small factory can only produce so many of the largely hand-built cars, so initial sales in the U.S. were to be limited to about five cars a year during 2012, the automaker said in February. After that, a planned factory expansion would allow for sales of as many as 10 cars a year here.

The Huayra, pronounced "why-rah," is named after the ancient Andean wind god Aymara Huayra Tata