"Ambassador Grenell resigned from his post and the State Department on June 1," said the spokesman.
Robin Quinville, deputy chief of mission at the embassy, will take over as Charge d'Affaires until a new ambassador is confirmed but the spokesman said any questions on Grenell's successor should be directed to the White House.
In his two years as ambassador, Grenell has not been shy to voice criticism of German policies on NATO and its involvement in the NordStream 2 gas pipeline from Russia.
Germany's dpa news agency reported last month that Grenell would step down soon after the U.S. Senate confirmed Representative John Ratcliffe, also a political ally of Trump, as the permanent director of national intelligence (DNI).In February, Trump had named 53-year old Grenell as acting DNI.