Germany's transportation minister said that US officials have complained about Volkswagen's cooperation over the past few months amid a global scandal engulfing the car giant.
Volkswagen is currently mired in controversy after admitting it had equipped 11 million of its vehicles with software designed to skew the results of pollution emissions tests.
In September, US regulators -- the Environmental Protection Agency (EPA) and the California Air Resources Board -- said Volkswagen could face an $18 billion penalty over the software made to meet clean-air standards during official emissions testing but which would intentionally turn off during normal operations.
"Our American partners have explicitly praised the cooperation and exchange of information with Germany," Transportation Minister Alexander Dobrindt told journalists at the German embassy in Washington on Tuesday, following a meeting with EPA officials.
But "at the EPA, there was criticism about cooperation with Volkswagen these past few months," he said, adding that the annoyance was clearly discernible and that it would take "considerable work" to rebuild a breach of trust.
"There's no sugarcoating it –- that's what our colleagues (at the EPA) told us very clearly," Dobrindt said.
An EPA spokeswoman said she did not have any details to share about the meeting.
Dobrindt is on a tour of the United States that will also take him to Michigan and California.
On Monday he met with his US counterpart, Transportation Secretary Anthony Foxx, to also brief him on the steps Berlin was taking to address the VW scandal.
During that encounter, Dobrindt offered to keep Washington posted on a regular basis and also invited US experts to visit Germany for a closer look at the technical steps underway to follow up on the affair.
Dobrindt said Foxx assured him that Germany would remain a strong auto industry partner for the United States.
"We are a welcome partner... This is specifically about one problem –- diesel motors and manipulation by Volkswagen," Dobrindt said.
When asked about fines, Dobrindt said that there had been no final determination on that point and that it appeared that US authorities were still in the analytical phase.