German automaker Daimler AG, which makes the Mercedes and Smart car brands in the U.S., said Friday it had launched an investigation, at the request of the U.S. Department of Justice, into how it measures diesel exhaust emissions. The carmaker was approached by USDJ last week, following a class-action lawsuit filed against the company in February.

In its statement, released Friday, Daimler dismissed the claims as being “without merit” and said it was cooperating fully with the authorities.

The announcement came in the same week which saw Japan’s Mitsubishi Motors admitting it had rigged data on some of its models' fuel efficiency, while France’s PSA Peugeot Citroen’s offices were raided by anti-fraud investigators as part of ongoing investigations in the auto industry.

Regulators and carmakers have increased their scrutiny of emission tests in the wake of the Volkswagen emissions scandal, which emerged in late September. The Wolfsburg, Germany company admitted to installing a computer software in its diesel cars which was designed to suppress emissions during tests, affecting about 11 million vehicles worldwide.

On Thursday, Volkswagen said it would buy back more than 500,000 diesel cars in the United States that used the emissions cheating software.

Meanwhile, in the U.K., authorities said a vehicle testing program had not uncovered any “evidence of car manufacturers, apart from the VW Group” of fitting devices to cheat on emissions test programs, according to a BBC report Thursday.