Lueneburg  Closing arguments expected in the German trial of a former SS officer known as the "bookkeeper of Auschwitz" were postponed Thursday due to the ill health of the 94-year-old defendant.

Presiding judge Franz Kompisch of the regional court in the northern city of Lueneburg said the accused, Oskar Groening, had unspecified "significant health problems".

The trial "cannot continue without him," Kompisch said.

Prosecutors had been slated to begin closing arguments on Thursday.

Groening had attended a hearing on Wednesday but declined to deliver a planned statement to the court because previous testimony had proved "taxing" for him, his defence team said. One of his lawyers read the statement for him.

As a heatwave sent temperatures in the courtroom soaring, Kompisch noted that Groening had seem "weak" on Wednesday and had not recovered, after a hearing in which 84-year-old Auschwitz survivor Irene Weiss described in searing detail how the Nazis had decimated her family.

"He is weaker than ever," the judge added, citing Groening's lawyers.

Kompisch had said he hoped to deliver a verdict by the end of July but noted Thursday that Groening's "shaky health" could scupper that deadline.

The judge rejected a defence motion to reduce hearings to one per week, following a decision in May to limit court appearances to three hours per day after repeated delays due to Groening's deteriorating condition.

The trial, expected to be one of the last of its kind, is now scheduled to resume on Tuesday.

Groening stands accused of 300,000 counts of "accessory to murder" in the cases of deported Hungarian Jews sent to the gas chambers between May and July 1944. He faces up to 15 years in prison.

He served as a bookkeeper at the camp, sorting and counting the money taken from those killed or used as slave labour, collecting cash in different currencies from across Europe and shipping it back to Berlin.

Since the trial opened in April, he has acknowledged "moral guilt" but said it is up to the court to rule on his legal culpability.

In the statement read out by his lawyers Wednesday, Groening said he did not feel entitled to ask Holocaust survivors to forgive him.

"I can only ask my Lord God for forgiveness," he said.