Wiesenthal passed away in his sleep at his home in Vienna, Austria, Rabbi Marvin Hier, the dean and founder of the Simon Wiesenthal Centre in Los Angeles, said.

"I think he'll be remembered as the conscience of the Holocaust," Mr Hier said. "When the Holocaust ended in 1945 and the whole world went home to forget, he alone remained behind to remember.

"He did not forget. He became the permanent representative of the victims, determined to bring the perpetrators of history's greatest crime to justice."

Wiesenthal, who was an architect before the second world war, dedicated himself to tracking down Nazi war criminals and being a voice for the 6 million Jews who died during the Holocaust. He lost 89 relatives in the atrocity.

"The task was overwhelming," Mr Hier added. "The cause had few friends. The Allies were already focused on the cold war, the survivors were rebuilding their shattered lives - and Simon Wiesenthal was all alone, combining the role of both prosecutor and detective at the same time."

Wiesenthal spent more than 50 years hunting Nazi war criminals, speaking out against neo-Nazism and racism and remembering the Jewish experience as a lesson for humanity. Through his work, he said, around 1,100 Nazi war criminals were brought to justice.

"With much energy and astonishing persistence, he refused to let the perpetrators of the single greatest crime of man against man go unjudged, unpunished, forgotten," Britain's chief rabbi, Sir Jonathan Sacks, said.

"In the early years, his was a lonely and much misunderstood mission, yet he continued to insist that what he sought was justice, not vengeance.

"The sheer scale of the task he undertook was immense. His moral clarity and courage were unfailing. All those who fight hate are in his debt."

The foreign secretary, Jack Straw, said Wiesenthal would "forever be rightly credited" with ensuring justice for some of the worst crimes in history was done.

"He was tireless in his efforts, and he gave the Jewish communities in the UK and around the world a lifetime of service. Future generations will forever be indebted to him," Mr Straw said.

Wiesenthal's quest began after the US liberated the Mauthausen death camp in Austria, where he was a prisoner, in May 1945. It was the fifth among the dozen Nazi camps in which he was imprisoned, and he weighed just 45kgs (99lbs) when he was freed.

"When history looks back, I want people to know the Nazis weren't able to kill millions of people and get away with it," he once said.

He said he quickly realised "there is no freedom without justice", and decided to dedicate "a few years" to seeking justice. "It became decades," he added.