A federal judge stripped a man of his citizenship because he hid his past as a guard at a Nazi labor camp and should never have entered the United States.

U.S. District Judge Paul Gadola agreed with government prosecutors who said Iwan Mandycz (search) was an armed guard at the Poniatowa labor camp (search) near Lublin, Poland, for nearly six months in 1943, the Detroit Free Press reported in Wednesday's editions.

The Justice Department first initiated denaturalization proceedings against Mandycz in April 2000.

"The government has proved by clear, unequivocal, and convincing evidence that defendant assisted in the persecution of civilian populations during World War II," the decision reads.

Mandycz, who is in his 80s, can appeal. If the ruling stands, the government could initiate deportation proceedings against him.

A message left Wednesday for Mandycz's lawyer, Joseph Siciliano, was not immediately returned.

"By standing guard to enforce the inmates' confinement under horribly inhumane conditions, Mandycz helped to ensure their systematic degradation and then their mass murder," Eli M. Rosenbaum, director of the Justice Department's Office of Special Investigations, said Wednesday.

Mandycz has denied working at the camp and has said he spent World War II working at his parents' farm in Poland and, later, as a forced laborer at a farm in Austria. He immigrated to the United States in 1949 and became a U.S. citizen in 1955. He has lived in the Detroit area ever since.

"There is no evidence that Mandycz harmed or attempted to harm anyone," defense attorney Andrew Haliw said in a court filing.

Haliw said Mandycz suffers from dementia and has been unable to assist in "any meaningful way" with the defense, although that is not a requirement in denaturalization proceedings.

Thousands of Jews and Soviet prisoners of war died or were killed at Poniatowa, including about 14,000 Jews who were massacred by the Nazis in a single day as they prepared to liquidate the camp.

The Office of Special Investigations started hunting down former Nazis in the United States in 1979. Since then it has won 79 cases and prevented more than 170 people with Nazi backgrounds from entering the country, the Justice Department said.