A court in the south-western German city of Baden-Baden said criticism from the Simon Wiesenthal Center in Jerusalem over its actions in the hunt for former SS doctor Aribert Heim is unfounded.

Court spokesman Heinz Heister rejected claims made last week by the Simon Wiesenthal Center chief Efraim Zuroff that a German judge had obstructed the hunt for Heim, and called the Zuroff allegation "defamatory."

Heister told Deutsche Presse-Agentur dpa that a German judge denied permission to tap the phones of Heim relatives because it had not satisfied criteria under German criminal-investigation laws, and this had been confirmed on appeal.

This setback was being taken out of context, he said.

"We are very committed to this investigation and are working intensively on it," the spokesman said, adding the German judges had mounted 11 requests since 2005 for foreign legal assistance as they try to track Heim down.

Heim, who performed gruesome, fatal experiments on concentration-camp inmates, vanished in 1962 as arrest loomed and is suspected to be still alive and living under an assumed name in Spain or Latin America.

Heim tops the list of the 10 most-sought Nazi criminals put out by the Simon Wiesenthal Centre in Jerusalem.

A member of the SS force, Heim was known for his sadism as a doctor at the Nazi's Mauthausen concentration camp in Austria. Heim is alleged to have killed hundreds of inmates in authausen with injections into their hearts. A total of 310,000 euros is being offered as a reward for his arrest.

There have been reported sightings of him over the years. If he is still alive, he would have celebrated his 94th birthday on Saturday.