Bosch says it is "defending its interests" in the long-running diesel saga and has asked US Courts to respect its staff privacy as allegations surrounding the supplier and Volkswagen continue to swirl.

Reports surfaced this week Bosch had rejected vehicles owners' claims in the US some of its personnel worked with Volkswagen to design technology allowing diesel vehicles to evade pollution-control tests.

"We take the allegation of manipulation of diesel software very seriously, but it is still [the] subject of investigation and civil litigation," a Bosch spokesman told just-auto from Stuttgart.

"We are cooperating with the investigation and various jurisdictions and we defend our interests in the litigation.

"We filed a request with the US court to respect employees' privacy interest as provided by US and German law.

"As a matter of policy, we can not further comment. We will not comment further concerning matters under investigation and litigation."

Bosch said last week it did not see the need to put more money aside for legal costs, leaving its provisions for such issues at EUR650m (US$731m).