"Polish staff members working for the center have lost access to classified information and had to be replaced," Foreign Affairs Minister Witold Waszczykowski was quoted as saying by the Radio Poland station. "In cases concerning changes in the military, such decisions are taken with immediate effect."
The raid was reportedly conducted by defense ministry officials accompanied by military police.
The Defense Ministry said in a press release on Friday that its spokesman and political cabinet director, Bartlomiej Misiewicz, had appointed Col.Robert Bala as acting chief of the NATO Counterintelligence Center of Excellence (COE).
Misiewicz tweeted hours later that the COE raid was "a matter for the Polish authorities."
Former Defense Minister and opposition party member Tomasz Siemoniak said the raid "is probably the first time in NATO’s history that an alliance member has attacked a NATO facility."
A NATO official told the station that the research center is staffed and funded on a national level, together with Slovakia, and is not "directly operated by NATO." The move is seen as an attempt by the new Polish government to consolidate its power.
The military alliance operates 24 COEs, described as international military organizations that train "leaders and specialists" from NATO member and partner countries, and are coordinated by the US-based Allied Command Transformation. Part of a wider framework supporting NATO Command Arrangements, the COEs are described as being outside the NATO command structure.