Anne Frank was refused sanctuary by the US

It casts new light on the wartime lives of Otto Frank and his family, who hid for more than two years from July 1942 in an annex in an Amsterdam warehouse before being arrested.

His daughter Anne described their life in hiding in a diary that has sold 75 million copies.

Her father's letters were released by the Yivo Institute for Jewish Research in New York after a volunteer found them among 100,000 other Holocaust-related documents.

Mr Frank wrote to family, friends and officials from April to December 1941.

He tried to arrange US visas for his family - wife Edith, daughters Margo and Anne and mother-in-law Rosa Hollander - before they went into hiding.

'I know that it will be impossible for us all to leave... but Edith urges me to leave alone or with the children,' he wrote to college friend Nathan Straus.

In another letter he wrote: 'I would not ask if conditions here would not force me to do all I can in time to be able to avoid worse.

'It is for the sake of the children mainly that we have to care for. Our own fate is of less importance.'

His efforts were hampered by restrictive American immigration policies designed to protect national security, Holocaust experts said. There were also nearly 300,000 names on a waiting list for an immigration visa.

Mr Frank's attempt to move his family mirrors the efforts of thousands of 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.'

Mr Frank stopped writing in December 1941 because Germany had declared war on the United States following the Japanese attack on Pearl Harbour.

After that the family went into hiding for two years until their arrest. Anne died of typhus at 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.