German Foreign Minister Sigmar Gabriel has ordered a "special inspection" into past irregularities in billing of expenses at its embassy in Paris, but the ministry said it was not aware of similar problems at other embassies.

Walter Lindner, a senior ministry official, disclosed the probe in a letter to Greens lawmaker Franziska Brantner dated Friday, and said it could trigger new recommendations for billing practices at all foreign offices.

The letter marked the first confirmation by the ministry of irregularities at the Paris embassy after French daily Le Monde reported that the embassy had set up an undeclared cash fund to pay staff for special events at the embassy for third parties.

In the letter, first reported by the Koelner Stadt-Anzeiger newspaper, Lindner said the ministry had revamped billing procedures in Paris in spring 2016 after discovering that the previous "form of billing had not met the usual standards."

The changes were triggered after a former butler and head waiter accused the embassy of using fake invoices to channel money into a fund used to give staff undeclared cash for overtime work at events hosted on behalf of private companies such as BMW and Mercedes.

Lindner said the changes implemented in Paris ensured "a transparent accounting of the use of the embassy by third parties," but the thorough review now underway could also trigger recommendations for all foreign missions and embassies.

Brantner urged the ministry to hold those accountable for the problematic billing practices in Paris - some of whom still worked for the ministry.

"In addition, all foreign offices must be carefully examined to ensure that such practices are not occurring elsewhere," Brantner said in a statement. She also called for protection of whistleblowers.