MUNICH Germany (Reuters) - John Demjanjuk, accused of helping to kill 27,900 Jews in the Holocaust, was forced to appear in court on Thursday after the 90-year-old had refused to attend the previous two sessions due to health reasons.

Judge Ralph Alt ordered Demjanjuk to appear on Thursday. He was rolled into the Munich courtroom on a hospital stretcher. "Yes, he was ordered to show today, and yes he showed," Alt told Reuters. He declined further comment.

Demjanjuk denies having worked at the Sobibor Nazi death camp in Poland. His family says he is too frail for trial, which he began in November in a wheelchair and attends lying down.

German media reported the trial could have collapsed if Demjanjuk did not appear in court for three consecutive weeks. He reportedly refused to allow himself to be transported from the Munich prison to the court.

Demjanjuk had been suffering from dehydration due to a heat wave. But he was pronounced fit again for trial before Thursday's forced appearance.

German state prosecutors accuse Demjanjuk, who was top of the Simon Wiesenthal Centre's list of most wanted war criminals, of assisting in killings at Sobibor, where they say at least 250,000 Jews were killed.

Demjanjuk was born in Ukraine and fought in the Red Army before the Nazis captured him and recruited him as a camp guard during World War Two. He emigrated to the United States in 1951 and became a naturalised citizen in 1958.

(Reporting by Annika Breidthardt; Editing by Jon Hemming)