The limousine involved in a crash that killed 20 people in upstate New York had failed inspection and the driver lacked proper license, New York Governor Andrew Cuomo said Monday.

The vehicle -- which was an SUV modified into a limousine -- "was inspected by the New York State Department of Transportation last month and failed inspection and was not supposed to be on the road," Cuomo told the press.

He also said the driver of the modified limo "did not have the appropriate driver's license to be operating that vehicle."

The stretch limo had been rebuilt in a way that violated federal law, the governor added.

The crash occurred on Saturday afternoon when the limousine "failed to stop" at an intersection in Schoharie, about 160 miles (about 257 km) north of New York City, and struck a parked vehicle.

At a press conference on Sunday, authorities said all the 20 victims were adults, including the limo's 17 passengers, the driver and two pedestrians.

Relatives said the group in the limo was headed to a birthday party.

Further investigation into the cause of the accident is underway.

Cuomo said in a statement on Sunday that he had directed state agencies "to provide every resource necessary to aid in this investigation and determine what led to this tragedy."

Investigators from the National Transportation Safety Board (NTSB) are assisting in the investigation.

NTSB Chairman Robert Sumwalt said at Sunday's press conference that the crash was "the most deadly transportation accident in this country since February 2009".