Russia says it is likely to cancel a landmark exhibition of Russian art in London because Britain had not guaranteed the paintings' return.The exhibition - "From Russia: French and Russian master paintings 1870-1925" - is scheduled to open on January 26 at the Royal Academy of Arts, featuring works from four Russian museums by Gauguin, Matisse, Renoir, Van Gogh and Russian artists.The exhibition consists of 120 paintings, including The Dance by Matisse.Russia says Britain is not guaranteeing the pictures' protection from legal claims on their ownership, and that the exhibition - currently in Germany - will likely have to be called off.Kremlin spokesman Dmitry Peskov told journalists: "The organisers of the exhibition could not guarantee that this exhibition would not be a subject for any legal attacks ... any unpleasant approaches that would endanger the return to Russia of those pictures.""If by Thursday morning the British Government does not give a final guarantee on the return of the paintings, the paintings will go to Russia," Natalia Ubarova, a spokeswoman for the federal Culture and Cinema Service, told Interfax news agency.Earlier Irina Antonova, director of the Pushkin Museum, told Interfax news agency that since negotiations "did not end successfully, the decision has been taken to return the whole exhibition to Russia."However a spokesman for the Department of Culture, Media and Sport in London said: "We have had no notification that the Russian galleries intend to change their plans to loan works.""The Government has done everything possible to facilitate the exhibition going ahead, including full assurances that the works would be protected from seizure," the spokesman said."We have also underwritten the collection against loss or damage to the value of nearly 900 million pounds ($2 billion)."Thousands of works of art are leant to exhibitions in the UK each year from foreign institutions, including Russia."Russian NTV television reports that former White Russians, whose property was seized after the Bolshevik Revolution, were among those who might target the artwork if it arrived in London.Anatoly Vilkov, the deputy head of the Russian Culture Ministry, told Echo of Moscow radio that the artworks would be allowed to travel if challengers to their ownership formally surrendered their claims, or if Britain's High Court issued a legal guarantee on the art's return.Mr Vilkov said "there is no politics" in the cultural spat.However the row adds to mounting British-Russian tensions, including Moscow's decision to close down British cultural offices in Russia and London's attempt to extradite a Russian man over the murder of a fugitive Kremlin critic last year."Unfortunately, really we are not living through the best period of our diplomatic relationship with Britain," Mr Peskov told journalists in a telephone conference call.