Anne Frank died in a Nazi concentration camp a month earlier than than previously thought, researchers announced on Tuesday - the 70th anniversary of the officially recognized date of her death.

The Jewish teenager likely died, aged 15, at the Bergen-Belsen concentration camp in February 1945, said the Amsterdam museum that honors her memory.

"New research...has shed fresh light on the last days of Anne Frank and her sister Margot," the Anne Frank House in Amsterdam said on Tuesday, until now her official date of death.

"Their deaths must have occurred in February 1945," the museum said in a statement.

The Red Cross noted that the deaths of Anne and Margot in the Bergen-Belsen concentration camp in northern Germany were between 1 and 31 March. Dutch officials then officially set the date at March 31.

Anne's diary about hiding from the Nazi's during the occupation of the Netherlands was published after World War II, becoming an international bestseller and making her an enduring symbol of Holocaust victims.

The new date changes little about the tragic lives of Anne and her sister Margot. "It was horrible. It was terrible. And it still is," said Erika Prins, a researcher at the Anne Frank House museum.

But, she added, the new date lays to rest the idea the sisters could have been rescued if they had lived just a little longer.

"When you say they died at the end of March, it gives you a feeling that they died just before liberation. So maybe if they'd lived two more weeks..." Prins said, her voice trailing off. "Well, that's not true anymore."

'One day they simply weren't there anymore'

Anne and her family went into hiding in 1942 from the Nazis in a secret annex at the back of an Amsterdam canal house, owned by her father Otto Frank's company, until they were betrayed in 1944 and sent to Germany.

The girls were moved from the Auschwitz-Birkenau concentration camp to Bergen-Belsen in November 1944, as the Russian army closed in from the east.

Researchers used Red Cross archives, the International Tracing Service and the Bergen-Belsen Memorial, together "with as many eyewitness testimonies and survivors as possible."

Four Bergen-Belsen survivors reported the sisters showed signs of typhus in late January 1945.

"Most deaths of typhus occur around 12 days after the first systems appeared," the new study said, quoting the Dutch National Institute for Public Health and the Environment.

"It is therefore unlikely that they survived until the end of March," the Anne Frank House said.

While Anne and Margot's date of death remains unknown, one surviving witness, Rachel van Amerongen said, "one day they simply weren't there anymore."

jlw/jr (AFP, AP, dpa, Reuters)