FRANKFURT (Reuters) - Germany has found no signs so far that Mercedes-Benz used illegal software to manipulate diesel emissions but a new round of tests is being conducted, the transport ministry said on Friday.

FILE PHOTO - The Mercedes-Benz logo is seen before the company's annual news conference in Stuttgart, Germany, February 4, 2016. REUTERS/Michaela Rehle/File Photo

The Transport Ministry summoned officials from Daimler, which owns the Mercedes-Benz brand, to a meeting on Thursday to explain why some vehicles showed high levels of emissions under certain driving conditions.

Engine management systems and software have come under scrutiny ever since Volkswagen admitted in Sept. 2015 that it had installed programs which cheat diesel emissions tests.

“It was agreed that Mercedes vehicles will be tested by the KBA,” a ministry spokesman said on Friday, adding that Daimler had been cooperative and had reiterated its vehicles conform with emissions regulations.

German magazine Der Spiegel on Friday said, without citing sources, that officials from the KBA, Germany’s vehicle certification authority, believe Mercedes-Benz may have diesel cars equipped with illegal cheating software.

Upon being asked about the report in Der Spiegel, Daimler said that based on the information it had at its disposal, it would fight allegations about using an illegal software defeat device with all legal means.

Upon being asked about whether KBA had found a defeat device in Mercedes cars, a KBA spokesman on Friday said, “We need to wait for the results of investigation to be published.”

KBA reports to Germany’s transport ministry.

Der Spiegel said that Germany’s Transport Ministry had threatened Mercedes with recalling vehicles equipped with OM642 and OM651 engines. Daimler said it could not comment on the contents of the meeting but denied there had been a threat of a forced recall.

Germany’s Transport Ministry also said KBA had not threatened Daimler with a recall.

In April last year, German Transport Minister Alexander Dobrindt said carmakers including Mercedes would voluntarily recall 630,000 diesel vehicles to change engine and emissions management software.

At the time, Dobrindt said regulators on the lookout for illegal emissions cheating software had found carmakers exploited a legal loophole to reduce emissions filtering systems.

Under certain circumstances carmakers are allowed to throttle back emissions management systems to protect the engine. Cars which start up when it is very cold outside run the risk of having condensation build up in their catalytic converters and engines causing rust.