Depeche Mode [ tickets ], who were forced to cancel their Tuesday (5/12) concert in Athens just minutes before going on stage when frontman Dave Gahan fell ill, has now pulled the plug on a total of six shows.

In addition to previously announced cancellations in Athens (5/12) and Istanbul (5/14), the group has crossed off its impending shows in Bucharest, Romania (5/16); Sofia, Bulgaria (5/18); Belgrade, Serbia (5/20); and Zagreb, Croatia (5/21).

The cancellations are the result of "further complications from singer Dave Gahan's severe bout of gastroenteritis," according to a press release, which went on to say that the singer "is currently undergoing further tests."

Ticketholders are advised to hold on to their tickets pending an announcement about rescheduled dates or final cancellations, according to Depeche Mode's website.

Gahan's health problems have derailed a world tour that just got underway last week. The outing--which supports the group's recently released album, "Sounds of the Universe"--is scheduled to hit US shores in July.