A survey of 50,000 travellers in key source markets has found 40% said terror threats will affect their travel plans for 2016.
The global survey, by tourism research institute IPK International, found 15% said they will not travel abroad in 2016 or will only go on domestic trips within their own country.
A further 25% said they will still be travelling abroad, yet only to destinations they perceive as safe.
But IPK said the results varied according to the region.
Unveiling the results at the ITB Convention in Berlin, IPK International CEO Rolf Freitag said: "With the recent terror attacks in popular holiday destinations such as Egypt and Turkey, as well as the attacks in Paris, the international tourism industry is looking at the travel year 2016 with quite some scepticism.
"Worldwide, international travel is expected to grow by 3% in 2016. Without the recent terror threats however, a growth of 4.5% would be possible."
But despite terror fears, international trips by Europeans are expected to continue on a slight upward trend.
"Demand appears likely to increase from the Netherlands, the UK, Switzerland and Germany – and is expected to fall from Russia, Greece and Italy," said IPK.
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