The French authorities have refused to allow a painting by the French impressionist, Claude Monet, to leave the country for fear it could be sequestered as an item plundered by the Nazis during the Second World War.

The painting, one of Monet's studies of water lilies, was due to be included in a major exhibition of his work at the Royal Academy in London.

Descendants of a French Jewish art-dealer, Paul Rosenberg, say it was looted from his collection during the German occupation.

Since 1974 the painting has been on show in a museum in Caen in France.

Investigations are underway into its ownership.

After the war, the painting was found in a warehouse in Hamburg, tagged as part of the collection of the Nazi Foreign Minister, Joachim von Ribbentrop.