Regulators in the U.S. and Europe are digging deeper into potential auto emissions irregularities.

Mercedes-Benz parent Daimler said Friday that the U.S. Department of Justice asked for an internal investigation into how it certifies exhaust emissions.

German officials, meanwhile, announced a sweeping emissions recall that will affect 630,000 diesel cars sold in Europe, including Audi, Mercedes-Benz, Opel, Porsche, and Volkswagen vehicles – but also European market Chevrolet, Ford, Jeep, and Land Rover vehicles.

The two events come as other regulators in Europe also are investigating emissions issues, and on the same day as Volkswagen disclosed it set aside $18 billion to deal with its ongoing Dieselgate scandal. VW admitted in September that it installed defeat devices in many diesel cars so that they would cheat emissions tests.

Earlier in the week the first details of a broad proposed settlement between VW, the U.S. government and plaintiffs’ attorneys were released in federal court. The company agreed to buy back or fix affected diesels, or let drivers walk away from their leases. VW also agreed to set up a fund to address the environmental impact of its excessive emissions.

"There are going to be more and more of these kinds of investigations," said Todd Turner, auto industry analyst with consulting firm Car Concepts.

"We're going to see more manufacturers being asked to provide documentation,” Turner said. “This is not so much saying something is wrong, just asking automakers to prove their math, that the procedures were proper and the results were double-checked."

Most of the inquiries focus on diesel engines.

"It is clearly difficult and expensive to make diesel cars meet emissions requirements," said Jake Fisher, director of auto testing at Consumer Reports. "What's unclear is how much of a future they have, as gasoline engines become more efficient and more electric and hybrid models prove themselves in the market."

In a statement about the Justice Department request, Daimler said it is “cooperating fully with the authorities. Daimler will consequently investigate possible indications of irregularities and of course take all necessary actions."

Daimler came under scrutiny two months ago when a class-action lawsuit in Illinois set off a flurry of similar suits accusing the automaker of putting defeat devices in its diesel models – rendering them less clean when speeds are below 50 mph. This alleged method of playing with the diesel systems means that, while emissions are more noxious, the engine gains more capability.

Daimler said the suit is "without merit."