John Demjanjuk arrives in court for his trial in Munich on Monday. (Matthias Schrader/Associated Press)

A frail John Demjanjuk arrived by ambulance Monday at a court in Munich to face allegations that he helped to kill 29,000 Jews as a guard at a Nazi death camp in 1943.

The trial commenced with the attorney for 89-year-old Demjanjuk filing a motion against the judge and prosecutors, accusing them of bias.

Demjanjuk was pronounced fit for trial in July, but his health condition means the court will be limited to two 90-minute sessions each day.

Following the day's first session, he returned to the courtroom on a gurney and wrapped in blankets. After Demjanjuk complained of pain, a doctor gave him an injection, and the afternoon session was ordered halted after only 30 minutes.

Demjanjuk faces up to 15 years in prison if he is convicted of the charges against him. The case is slated to last through May.

Prosecutors allege Demjanjuk was a guard at the Sobibor camp in Nazi-occupied Poland in 1943, where they say he was complicit in the murders of Jews.

Demjanjuk, who was born in Ukraine and after the war moved to the United States where he worked at an auto plant near Cleveland, has denied any role in the killings. He says he was a Red Army soldier who spent the Second World War as a Nazi prisoner of war.

Demjanjuk's lawyer, Ulrich Busch, claimed that the court and prosecutors are treating foreign-born guards more harshly than the German officers who commanded the camps.

Busch said the case should never have been brought to trial, citing others where guards at Sobibor were acquitted.

"How can you say that those who gave the orders were innocent … and the one who received the orders is guilty?" Busch demanded. "There is a moral and legal double standard being applied today."

With files from The Associated Press