Citing a report by the German weekly Die Zeit, Haaretz said Saturday the sources insist pages from Kafka's 1919 work are being stored in the safe by Chava Hoffe, who is facing a lawsuit by the National Library in Jerusalem.
The National Library wants Hoffe to give up possession of the Kafka archives. Hoffe's mother was given the archives after serving as secretary to Kafka's friend, Max Brod.
The Zurich safe and its contents are expected to become part of the dispute over ownership of the Kafka archives.
Haaretz said, again citing Die Zeit, Brod wrote a letter as early as 1945 in which he leaves the valuable literary archives to Hoffe's mother, Esther.
While the National Library's claim to the archives could prove unfounded if the date of the letter is legitimate, an attorney for the Jerusalem library disputes the date.
"The secrecy surrounding the Zurich safe speaks for itself -- if the Hoffes are the rightful owners, what do they have to hide?" Jerusalem National Library attorney Meir Heller asked.