Belgian police and German investigators carried out a raid on Tuesday at the headquarters of the centre-right European People's Party (EPP) as part of an investigation in Germany.
The party, which has the most members in the European Parliament, said in a statement that representatives of authorities from Belgian and Germany had visited its headquarters in Brussels on Tuesday.
The visit related to an investigation in the German state of Thuringia, the statement said, without elaborating.
"The party is cooperating in full transparency with the authorities involved, providing all relevant information and documentation," the EPP said in a statement.
Further information could not be revealed as the investigation in Germany was ongoing, it said.
According to the Thueringer Allgemeine newspaper, the raid was in relation to an ongoing corruption investigation into Mario Voigt, the leader of the central state of Thuringia's Christian Democrats, over his role in the EPP's digital election campaign in the 2019 European elections.
The investigation centres around allegations that Voigt received kickbacks from an internet company that was awarded a contract during the campaign, the paper said.
Voigt's lawyers rejected prosecutors' allegations as groundless and called the investigation excessive.
Prosecutors in Thuringia were not available for comment.
The EPP has parties across the 27 EU members and others outside the bloc, such as in the western Balkans, Norway, Switzerland and Ukraine.
(Reporting by Philip Blenkinsop and Joern Poltz;Editing by Bernadette Baum and Ed Osmond)
