Documents released by the Labour Party confirmed that the Prime Minister was "lying" when linked deputy leader Mario de Marco to an undeclared company in Cyprus.
The documents show that Dr de Marco was a director in the company owned by an Irish national.
"Joseph Muscat certainly knows the difference between owning a company and being a director of it," a statement by the Nationalist Party said.
The Cypriot company called Twinkleday Ltd was registered and located in Malta and registered with the Malta Financial Services Authority. The facts may be verified by a simple search on the MFSA site.
Mario de Marco declared he was one of the directors of the company through a declaration of assets in Parliament between 2013 and 2016, with such declarations accessible to the media, the PN said.
"This is an example of desperation gripping Muscat through which he is getting caught up in his own lies."