Researchers have discovered a previously unknown cache of papers related to Anne Frank (centre), one of the most famous victims of the Holocaust.

The documents show that Otto Frank tried to get his daughters Margot and Anne out of Nazi-occupied Europe before it was too late. He wrote to a friend in the US for help.

The friend, Nathan Straus, tells Frank he is trying to help - but for visas, they must get from Amsterdam to an American Consul in Portugal, Spain, France or Switzerland.

Straus also turned to the National Refugee Service, a private organisation, to try to aid the Frank family.

But the service privately doubted whether the US would give visas to children whose parents remained behind in occupied Europe.

The Dutch Jewish Council also tried to help, seeking a way to get Otto Frank to neutral Cuba.

All efforts to get the family out failed, and they went into hiding in 1942. They were discovered and sent to concentration camps. Only Otto survived.