Ancient bronze vessels and other items, repatriated from Germany, Belgium and Britain, are displayed at the National Archaeological Museum in Athens on Tuesday. (Associated Press)

Greece unveiled hundreds of looted antiquities on Monday, saying they had been returned by Germany, Belgium and Britain.

Among the items displayed at the Archaeological Museum in Athens was an 11th or 12th century marble fragment, which Culture Minister Antonis Samaras said had been returned from Britain.

A family member of a British tourist who took the piece from a Byzantine temple in the 1950s had returned the fragment to the Greek Embassy in London, Samaras said.

Greece is stepping up pressure on the British Museum to return the Elgin Marbles, ahead of the opening of the Acropolis Museum in June.

The British Museum has refused to repatriate the fifth-century marbles, saying Lord Elgin removed them from the Acropolis legally, with the blessing of the Ottoman Empire that then ruled the region.

Athens plans to open its 100-million-euro ($157-million Cdn) museum at the foot of the Acropolis on June 20.

It argues the marbles will have a suitable home in the new museum where they can be seen by thousand of tourists.

Italy offered two Parthenon fragments to the new Acropolis museum last year.

Greece also has reclaimed antiquities from the J. Paul Getty Museum in Los Angeles and the Shelby White collection in New York.

A fifth-century coin and other artifacts returned from Belgium were displayed at the Archaeological Museum in Athens on Tuesday.

Artifacts from Germany included third-century copper and ceramic pots and vessels that were seized by customs officials in Nuremberg, Germany, in 2007. They were being smuggled into the country from Thessaly in northern Greece.

"Many of these items were returned with the co-operation of German authorities and the Greek consul general in Munich," Samaras said.