Anne Frank's father tried to arrange U.S. visas for his family before they went into hiding, but his efforts were hampered when Allied and Axis countries tightened immigration policies, according to papers released Wednesday.

Otto Frank also sent desperate letters to friends and family in the U.S. pleading for help with immigration costs as the family tried to escape the Nazi-occupied Netherlands.

"I would not ask if conditions here would not force me to do all I can in time to be able to avoid worse," Otto Frank wrote to his college friend Nathan Straus in April 1941. "It is for the sake of the children mainly that we have to care for. Our own fate is of less importance."

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The letters, along with documents and records from various agencies that helped people emigrate from Europe, were released by the YIVO Institute for Jewish Research, a New York-based institution that focuses on the history and culture of Eastern European Jews. The group discovered the file among 100,000 other Holocaust-related documents about a year and a half ago.

The documents show how Frank tried to arrange for his family — wife Edith, daughters Margo and Anne and mother-in-law Rosa Hollander — to go to the U.S. or Cuba. He wrote to relatives, friends and officials between April 30, 1941, and Dec. 11, 1941, when Germany declared war on the U.S.

But immigration rules were changing under the Nazi regime and in the U.S. There were nearly 300,000 people on a waiting list for a U.S. immigration visa. Besides, since Frank had living relatives in Germany, he would have been unable to immigrate under U.S. policy at the time.

"I know that it will be impossible for us all to leave even if most of the money is refundable, but Edith urges me to leave alone or with the children," he said in another letter to Straus.

He managed to secure one visa to Cuba, but it was canceled in December 1941 after the Germans declared war on the U.S. The family went into hiding in July 1942.

Otto Frank's attempt to move his family mirrors thousands of German Jews, said Richard Breitman, an American University professor who focuses on German and American intelligence history.

"Frank's case was unusual only in that he tried hard very late and enjoyed particularly good or fortunate American connections. Still, he failed," Breitman said.

The family was in 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 family's hiding place in a secret annex in an Amsterdam canal-side warehouse has been turned into a museum.

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.