Germany's highest court has turned down an appeal from suspected Nazi death camp guard John Demjanjuk.

The decision on Wednesday by Germany's constitutional court clears the way for the formal trial to begin next month in what is likely to be Germany's last major trial for war crimes committed in the Nazi-era.

Ukrainian-born Demjanjuk, 89, is charged with helping to kill almost 28,000 Jews at the Sobibor death camp in Poland.

He was deported from the US in May and has been in jail in Munich since then awaiting trial.

In July the court had rejected another appeal by Demjanjuk that his deportation from the United States infringed his basic rights.

Demjanjuk spent years in custody in Israel after he was extradited there in 1986, and was sentenced to death two years later after a court found him guilty of war crimes and crimes against humanity.

But in 1993 that verdict was overturned when Israel's supreme court ruled he was not the feared death camp guard known as "Ivan the Terrible".

His family insists he is innocent of all accusations and say that he is too ill to stand trial.