Dozens of letters found in an American archive reveal the desperate efforts of Anne Frank's father Otto to escape from the Nazis with his family.
The letters - including some from his American relatives and friends - were written before the family went into hiding in Amsterdam in 1942.
The 78 documents are to be released on 14 February by the YIVO Institute for Jewish Research in New York.
The family went into hiding in a cramped attic in Amsterdam during the Nazi occupation in July 1942 but a betrayal led to their arrest in 1944.
The letters were found in New York a year ago by a YIVO researcher, Estelle Guzik. They reveal how in 1941 Otto Frank had tried to obtain visas for his family to travel to the US or Cuba.
YIVO's executive director Carl Rheins said the documents covered the period from April 1941 to 11 December, 1941, when Nazi Germany declared war on the US.
Otto Frank urged a former university friend, Nathan Straus Jr of New York, to appeal to refugee agencies in the US to get the Frank family out.
"By July 1941 it is clear that Otto Frank had hit a stone wall," Mr Rheins told the BBC News website.
Otto Frank had also sought an escape route to Cuba, but in 1941 "it was very difficult to leave Holland," Mr Rheins said.
The family would have needed exit visas from the German authorities and then more visas to cross France and Spain, he said.
The file at YIVO also contains letters written after the war by Otto's brother-in-law Julius Hollander, revealing his efforts to locate the family.
YIVO publicity officer Cathy Callegari said the new information was "compelling" and had been authenticated by Holocaust experts.
Two leading historians of the Holocaust - professors Richard Breitman and David Engel - will present the letters and explain the historical background at the 14 February press briefing, YIVO says.