A Jewish family have claimed that the famous Birds' Head Haggadah, the oldest illustrated Passover manuscript, was stolen from their family by the Nazis.

The grandchildren of one of the first Jews captured by the Nazis have said that the 14^th Century Haggadah, which is currently on display at the Israel Museum in Jerusalem, was unlawfully sold to the museum 70 years ago.

The family have enlisted E Randol Schoenberg, who restored the Gustav Klimt paintings to their Jewish heir, to help them secure compensation for what they called "longstanding illegal and moral injustice".

They have agreed that the manuscript, which tells the biblical story of the exodus from Egypt, can remain in the Israel Museum, where it is currently being displayed in an exhition curated in the run-up to the passover.

They have asked that the museum pay the family compensation and rename it after them, otherwise they will face a lawsuit.

"We want a compromise," said Eli Barzilai, 75, who is leading the legal challenge from Jerusalem, on behalf of his cousins who live in Berlin and the US.

He said the manuscript is so rare, its value is priceless. Neither he, nor the family's lawyer would cite an exact figure they are seeking.

"If we go to court there's no turning back," said Barzilai.

The manuscript has been intriguing to academics due to its unusual illustrations, which include birds' heads.

It is "as myserious as the Pyramids of Giza, the monoliths of Easter Island, or Mona Lisa's smile", according to Marc Michael Epstein, a Vassar College professor and author of the book The Medieval Haggadah.

Barzilai said the manuscript was a gift from his grandmother's family to his grandfather, Ludwig Marum, for their wedding.

Marum was a lawyer who opposed Hitler and served in Germany's government. The Nazis paraded Marum in the town of Karlsruhe, before taking him to Kislau concentration camp, where he was murdered.