The card, bearing the signature of the schoolgirl who hid from the Nazis for years in an Amsterdam house before being caught, was sent in 1937 two years before war broke out.

It was addressed to Samme Ledermann, one of Anne's best friends, and postmarked from Aachen, a town just across the Dutch border in Germany, said Maatje Mostard, of the Anne Frank Museum.

The postcard, with a picture on the front of a Christmas-decorated bell in the foreground and a snow-covered field behind it, was signed "Anne Frank" with no other hand-written message. Ms Mostard said it was the second such card the museum had seen. "We know it's an original," she added.

Teacher Paul van den Heuvel found the Christmas greeting in a box of cards in the shop owned by his father in the town of Naarden, 10 miles east of Amsterdam.

He was gathering material on Anne Frank for his school to mark Liberation Day, the May 5 anniversary of the end of German occupation, when he came across the card.

The museum, which encompasses the small Amsterdam apartment where the Frank family hid from the Nazis for 25 months, has the largest collection of documents and papers on Anne Frank, whose diary is the most widely read book relating to the Holocaust.

Anne, her parents and sister and four other Jews hiding in the apartment were arrested in August 1944 and deported to Auschwitz. The sisters were later sent to the Bergen-Belsen concentration camp where Anne died of typhus in March 1945, two weeks before the camp was liberated. She was 15.