Poland's new conservative government on Friday continued a controversial drive to replace senior officials with its own appointees when it raided a NATO counter-espionage centre in Warsaw and fired its senior staff.

Colonel Krzysztof Dusza, the sacked head of the Counter Intelligence Centre of Excellence, said defence ministry officials and military police raided the joint Polish-Slovak centre in the early hours of Friday.

"I told them their presence here was illegal. When they left, I asked the police to put seals on the door," Dusza told public television, adding he had informed Slovakia "and other foreign partners".

The defence ministry issued a terse statement on the incident, saying only that it had installed a new interim director, Colonel Robert Bala.

In office since November, the new administration has already sparked uproar with its attempts to replace constitutional judges, a move that triggered mass protests.

Dusza insisted he was still at the helm because a joint Polish-Slovak decision was necessary to oust him.

"We expect a thorough clarification of the situation from our Polish partners," said the Slovak defence ministry, adding it was following the affair "very closely".

Polish deputy defence minister Bartosz Kownacki told local media the centre's officials had been sacked a week ago but held on "illegally to their posts, rejecting orders."

Foreign Minister Witold Waszczykowski told public radio they "had lost the right of access to confidential documents and should be replaced by others who have such rights."

Former defence minister Tomasz Siemoniak apologised on behalf of Poles to Slovakia over the raid, dubbing it "an absolute scandal" and "an unprecedented act in a NATO member country."

Antoni Macierewicz, the current defence minister and a hardliner within the ruling conservative Law and Justice (PiS) party, is reputed to have carried out extensive purges in the military intelligence services in 2006 when he was deputy defence minister.

Designed to expand NATO's intelligence-gathering capabilities in the light of new threats, especially from Russia, the Polish-Slovak centre was formally endorsed by NATO in October.

But a NATO official in Brussels told AFP that Friday's raid on the military centre was a uniquely Polish affair as the centre "has not yet been accredited by NATO."

"In general terms, Centres of Excellence are international research centres, which are nationally or multi-nationally funded and staffed, and work alongside the Alliance, but they are not NATO bodies," said the official, who did not wish to be named.

The centre's headquarters are located in Warsaw> The southern city of Krakow is scheduled to host the unit eventually.

Slovakia, Poland's neighbour to the south, is to also to host a branch.

Poland joined NATO in 1999 and Slovakia followed suit in 2004.