Officials in western Austria say exhumations are to take place at a psychiatric hospital thought to contain the remains of Nazi victims.
The remains of 220 people are buried at a cemetery in Hall in Tyrol province.
The Nazis murdered thousands of disabled people they thought unfit to live, deeming it "euthanasia". The hospital believes many died there as part of the programme.
A planned construction project has been halted to allow a full investigation.
Some 30,000 people were killed at one psychiatric hospital alone - Schloss Hartheim, near Linz in upper Austria.
Tilak, the company responsible for the Hall hospital, said the graves contained the remains of people buried between 1942 and 1945.
There were, it added, "suspicions that the dead [were] at least partially victims" of the programme of murders the Nazis referred to as "euthanasia".
'Dark chapter'
Exhumations are to begin when the ground thaws, probably in March.
Announcing that a commission of experts would be formed shortly to investigate, Guenther Platter, governor of Tyrol province, said he had been "deeply shaken" by the discovery.
"This dark chapter of history must now be carefully brought to light," he added.
Investigators would be seeking to identify the remains and establish the cause of death, Tilak representatives were quoted as saying by Austria's Die Presse newspaper.
Hospital historian Oliver Seifert said it was already clear that not all of those buried had been victims of the Nazis.
"We know that active killing went on at other institutions in Austria... but there are no indications of this at the moment in Hall," he told Reuters news agency.
Hall Hospital remains a functioning psychiatric hospital, with beds for 500 patients.
BBC News
