KAISERSLAUTERN, Germany — German authorities are looking into allegations that government employees and private contractors fraudulently billed for construction projects at Ramstein Air Base.

The Kaiserslautern prosecutor’s office is looking into accusations that 10 people — a mixture of Rhineland-Pfalz government workers and contractors — charged for base construction work that they did not perform, said Helmut Bleh, the city’s leading senior public prosecutor.

An anonymous letter dated April 22 alleging that the group bilked U.S. and German governments of millions of dollars sparked the office’s investigation, Bleh told Stars and Stripes. The German magazine Der Spiegel also received the letter and reported about it in its April edition.

Bleh cautioned that there have been no arrests and the investigation is ongoing.

“We do not have too much that can be confirmed right now,” he said, adding that he did not know how long the investigation could last.

1st Lt. Elizabeth Culbertson, a spokeswoman for the U.S. Air Forces in Europe headquarters command at Ramstein, said the Air Force could not comment about the investigation or reports about the allegations because the matter is being investigated by German authorities.

The U.S. and German governments are spending about $500 million to expand runways at Ramstein and Spangdahlem Air Base to make way for the increase in traffic due to the closure of Rhein-Main Air Base.

The U.S. military plans to turn over Rhein-Main in Frankfurt by the end of the year.