The Nazi-hunting Simon Wiesenthal Centre launched a new attempt yesterday to find and prosecute death camp guards believed to be among the conflict's last living war criminals to have escaped justice.

Announcing the campaign in Berlin – called Operation Last Chance II – the centre said it would offer a reward of up to £21,000 to anyone providing information leading to a conviction.

Dr Efraim Zuroff, the centre's chief Nazi hunter, said Germany's conviction of former death camp guard John Demjanjuk, 91, earlier this year set a legal precedent allowing hundreds of dormant investigations to be reopened.

"The Demjanjuk conviction has totally changed the situation," Mr Zuroff said. The verdict opens the way for the arrest of people involved in mass murder who were totally ignored until today."

In May, a Munich court convicted Ukrainian-born Demjanjuk of being an accomplice to the murder of more than 28,000 mainly Dutch Jews at the Sobibor extermination camp in Nazi-occupied Poland.

The case was the first in Germany in which a suspected Nazi war criminal had been found guilty on the basis of having served as a death camp guard but without evidence of a specific crime.

Mr Zuroff said the verdict meant German prosecutors could now track down and convict scores of other camp guards who had committed crimes against humanity.

He admitted, however, that of around 4,000 guards who worked in the death camps of Treblinka, Sobibor, Belzec and Chelmno, only 80 were thought to be still alive and of those, probably only 40 were fit enough to face trial.