FILE PHOTO: An illuminated Porsche logo is pictured on a building of a Porsche retail centre in Niederwangen, Switzerland, March 9, 2012. REUTERS/Michael Buholzer/File Photo

FRANKFURT/HAMBURG (Reuters) - Diesel models of Volkswagen's VOWG_p.DE sports car maker Porsche PSHG_p.DE have much higher emissions than is legally allowed, German weekly Der Spiegel reported on Friday, citing test results.

The magazine asked German test institute TUV Nord to check emission levels for the Porsche Cayenne V6 TDI, an SUV model, under normal driving conditions.

“Emissions in this test were higher than the limits for this type of car,” the magazine quoted the head of testing at TUV Nord Helge Schmidt as saying.

“With these values the car would not have been approved by the authorities,” Schmidt said.

Porsche said in a statement that it had received and studied the test results from Spiegel. “For us they are not comprehensible,” Porsche said.

The company said that emissions depend on several conditions such as engine load, speed and temperature.

There has been growing scrutiny of diesel vehicles since Volkswagen admitted in September 2015 that up to 11 million of its vehicles worldwide had software installed that cheated emissions tests.

VW was sentenced in April after pleading guilty in the emissions scandal. VW has agreed to spend up to $25 billion in the United States to address claims from owners, environmental regulators, states and dealers and offered to buy back about 500,000 polluting U.S. vehicles.

Volkswagen’s Audi unit is also under investigation.