But the disclosures were just part of a wider, concerted probe into Russian interference in the European Parliament (EP) by European intelligence services, involving also Belgium's VSSE domestic spy agency.

Disciplinary action must be swiftly taken against any MEPs or [EP election] candidates involved," said the office of Liberal French MEP Valérie Hayer, who first called for the EP discussion.

"A full and transparent internal investigation by the president of the European Parliament is now needed," her office added.