Austria's president has condemned the repeated destruction of photos of Holocaust survivors exhibited on a central Vienna street.

Alexander van der Bellen tweeted Monday that he was "deeply concerned" by the vandalism.

The Austrian news agency APA reported that the larger-than-life portraits of Holocaust survivors were defaced for the third time. In the most recent attack, The photos were cut across the faces of the survivors late Sunday night. Previously, several photos were daubed with swastikas and other graffiti.

The works by German-Italian photographer Luigi Toscano opened on part of the Ringstrasse, a busy road that runs around downtown Vienna, on May 7. Three Austrian groups announced they would hold around-the-clock vigils to prevent further attacks. The exhibit closes on May 31.