Passengers walk at Bulgaria's Burgas airport in this August 3, 2007 file photo. An explosion in a bus carrying Israeli tourists which killed at least four and injured dozens at the Bulgarian airport of Burgas on July 18, 2012 was a deliberate attack, national radio BNR quoted Interior Minister Tsvetan Tsvetanov as saying. Picture taken August 3, 2007. REUTERS/Nadezda Chipeva/Files (BULGARIA - Tags: DISASTER TRANSPORT) | Foto: Reuters