Five paintings by British expressionist artist Francis Bacon worth an estimated €30 million have been stolen from the private collection in Madrid, El Pais reported Sunday.

El Pais quoted the sources as saying the artworks of the Irish artist were stolen last June and the investigation is underway. The paintings are believed to have belonged to a 59-year-old friend of Bacon, who died in Madrid in 1992.

In their turn, the experts note that it is also unclear exactly which paintings are involved but they will be extremely difficult to sell. According to law enforcement officials, the stolen canvases have not been taken out of the country.