The Sofia Zoo has closed for visitors at the peak of the holiday season to investigate the mysterious deaths of five rare animals over the last few days.

Zoo director Ivan Ivanov said Tuesday three gaurs, one camel and one yak had died but refused to elaborate on the possible cause of the deaths.

Blood samples from the dead animals have been sent for testing and results are due by the end of this week.

Recently, authorities reported that some 3,000 animals have died from Bluetongue disease across the Balkan country, but experts said the symptoms of the zoo animals were different.

"Although there is no reason to worry of an epidemic, it would be unpleasant if animals start dying in front of the visitors," Ivanov said.