The work could be worth up to 50 million euros ($54 million), Bulgarian National Radio reported, citing experts.

Several people, including Bulgarian citizens, were arrested in the international operation, state news agency BTA reported on Tuesday.

The report did not give a description of the painting or any other details on the work.

Pollock, a major figure in the abstract expressionist movement of the 1940s and 50s, was known for his technique of pouring, dribbling and dripping paint in wild patterns onto large canvases. He died in 1956.

“This is an international operation with the participation of Europol, Greece and other countries,” Petar Todorov, Bulgaria’s Chief Secretary of the Ministry of Internal Affairs, said, according to the Novinite news agency.

“To our great joy, we managed to establish and keep this painting and at the moment the expertise shows that it is an original.”

(Reporting by Alan Charlish and Anna Wlodarczak-Semczuk in Warsaw; Editing by Andrew Heavens)