FRANKFURT (Reuters) - German prosecutors, who searched Daimler's offices this week as part of an investigation into diesel pollution, are talking to U.S. authorities, the Stuttgart public prosecutor's office said on Wednesday.

"We are in contact with U.S. authorities," the Stuttgart public prosecutor's office said, declining to elaborate further about the nature of potential cooperation and whether extensive searches of Daimler's offices in Germany had also been conducted at the behest of requests from U.S. regulators.

Stuttgart-based Daimler, owner of the Mercedes-Benz brand, said it was fully cooperating with authorities, and had been in touch with both German and U.S. authorities probing potential diesel emissions violations.

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"As part of our cooperation with authorities, we have made the same information available to the Stuttgart prosecutor and the U.S. authorities," a spokeswoman for Daimler said.

Daimler said it could not comment further given the ongoing nature of the probes.

Carmakers across the world have faced increased regulatory scrutiny over anti-pollution tests since Volkswagen AG (VOWG_p.DE) admitted in September 2015 to installing secret software allowing its cars to emit up to 40 times legally allowed pollution levels.

On Tuesday, the U.S. government took a tougher line against Fiat Chrysler by filing a civil lawsuit accusing the carmaker of illegally using software to bypass emission controls.

The prosecutors had searched Daimler's offices and other premises on Tuesday in the course of investigations "against known and unknown employees at Daimler who are suspected of fraud and misleading advertising connected with manipulated emissions treatment of diesel passenger cars."

Some 23 prosecutors and around 230 staff, including police and state criminal authorities, were involved in searches of 11 German sites, including Daimler offices, seeking data files and evidence.

No board member at Daimler has been implicated in the probe, the prosecutor's office said.

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Earlier this year, after the U.S. Environmental Protection Agency issued a notice of violation against Fiat Chrysler, Daimler warned that steps by U.S. authorities to investigate functionalities, including some which it said were common in diesel vehicles, could lead to significant penalties and vehicle recalls.

Daimler said in its first-quarter financial report that "it cannot be ruled out that the authorities might reach the conclusion that Mercedes-Benz diesel vehicles have similar functionalities."

(Reporting by Ilona Wissenbach; Writing by Edward Taylor; Editing by Maria Sheahan and Jane Merriman)