Retired U.S. autoworker John Demjanjuk on Thursday appealed his conviction and death sentence for Nazi war crimes, his attorney said.

Demjanjuk, 68, was sentenced to death on April 25, a week after being found guilty of being "Ivan the Terrible," a brutal guard who operated gas chambers that killed 850,000 Jews at the Treblinka death camp in Nazi-occupied Poland.

The Ukrainian-born Demjanjuk claims he is a victim of mistaken identity.

Israeli attorney Yoram Sheftel said the appeal asks the Supreme Court to reverse the conviction "due to lack of proof and much more than substantial doubt."