"We have come across the file which belonged to Otto Frank, documenting his efforts to immigrate his family and get them out of Holland," she said.
On Feb. 14, she said, the institute will release Frank's letters and documents and records from various agencies that helped people emigrate from Europe.
The disclosure came as a surprise to Bernd "Buddy" Elias, Anne Frank's cousin and the president of the Anne Frank Foundation in Basel, Switzerland. The organization, established by Otto Frank, holds the rights to Anne Frank's writings, according to its website.
"We would love to have them in our archive. I mean, we are the heirs of Otto Frank," Elias said.
Callegari said the documents include letters that Otto Frank wrote to relatives, friends, and officials between April 30, 1941, and Dec. 11, 1941, when Germany declared war on the United States .
The Frank family's hiding place in a secret annex in an Amsterdam canal-side warehouse has been turned into a museum.
Patricia Bosboom of the Anne Frank House museum said officials there had heard about the discovery of the letters but had not seen them. But she said they would fit with the general picture that is known about Otto Frank's many efforts to get the family out of Europe.
It also fits with Frank's other contingency planning: the family's hiding spot. "He organized it well before the war," she said.
The letters document how Otto Frank tried to arrange for his family -- wife Edith, daughters Margo and Anne, and mother-in-law Rosa Hollander -- to go to the United States or Cuba.
His attempts to arrange a route out of the Netherlands were unsuccessful. The family took refuge in July 1942, hiding for more than two years before being arrested. Anne Frank described the family's life in hiding in a diary that has sold an estimated 75 million copies.
The letters were initially held by the New York City-based Hebrew Immigrant Aid Society, which gradually transferred its archives to the YIVO Institute in 1974. Callegari said the HIAS archives consisted of documents from various agencies, so the true origin of the Otto Frank letters may never be known. She said a volunteer archivist at the YIVO Institute discovered Otto Frank's letters about a year and a half ago.
Anne Frank died of typhus at age 15 in a concentration camp at Bergen-Belsen, Germany, in 1945. Her father returned to the Netherlands to collect his daughter's notes and published them in the Netherlands in 1947.
For more information, go to the websites of the YIVO Institute for Jewish Research at www.yivo.org and the Anne Frank Foundation at www.annefrank.ch .
