The number of foreign visitors arriving in Turkey in June fell by 40.9 per cent, compared to the same month last year, as arrivals from Russia all but stopped and visitors from Germany dropped by more than a third.
Turkey's tourism sector has been hard-hit by terrorism concerns, political instability in the country as well as global headwinds.
This month's failed coup attempt may well have added to the damage.
The airline Swiss confirmed Thursday that it will halt its flights from Zurich to Istanbul during the upcoming winter season.
Swiss cited the worsening security situation that has resulted in dwindling passenger numbers, as well as overcapacities on this route.
US carrier Delta had announced earlier that it would suspend its service from New York to Istanbul that had been due to start in May, "due to increased security concerns in Turkey" as well as weaker demand.
For 11 straight months there have been steady, significant drops in the number of foreign visitors, Tourism Ministry figures show.
Numbers of visitors from all major European and global economies - from the US to Japan - saw double-digit declines in June, the worst month yet in the current tailspin.
Russian tourism fell off a cliff after Turkey downed one of Russia's fighter jets near the Turkish-Syrian border last year. The two countries recently reconciled and Moscow lifted a ban on charter flights to the country.
Russian arrivals dwindled by 93 per cent in June, while the numbers of Germans, who make up the biggest national group, fell 38 per cent.
Overall numbers in May were down nearly 35 per cent, while April saw figures lower by 28 per cent.
A spate of suicide bombings in Turkey this year, especially ones in tourism-heavy areas of Istanbul, have been one of the main reasons visitors are staying away so far. Renewed conflict in Turkey's mostly Kurdish south-east has also created concerns.