There are international train services to/from Bulgaria, Romania, Serbia, Iran and Austria.
Bosphor Express (Istanbul-Sofia, started departing from Halkali Station in Istanbul)
Bosphor Express (Istanbul-Bucharest, run during summer)
Bosphor Express (Istanbul-Belgrade, run during summer)
Optima Express (Villach-Edirne, runs during April-November)
Istanbul – Thessaloniki Train (cancelled)
Transasia Express (Ankara-Tehran, suspended)
Van – Tabriz Train (suspended)
Tehran – Van – Damascus Train (cancelled)
Gaziantep – Musul Train (cancelled)
Gaziantep – Aleppo Train (cancelled)
Tickets can be bought from stations, online ticket is not possible.