The final figures are not due to be published until spring but early estimates put the European countries in the top spots.
Spanish Prime Minister Mariano Rajoy recently announced a record number of international visitors to the country in 2017, totalling more than 82 million.
He said this led to a 12 per cent rise in earnings in the tourism sector to €87bn (£77bn).
Meanwhile, Donald Trump's first year as president of the US has been mired in controversy, from the decision to pull out of the Paris climate agreement to the on-going war of words with North Korea.
Tourist numbers dropped five per cent in the first quarter of 2017 and three per cent in the second quarter.
The UNWTO said: "Led by Mediterranean destinations, Europe recorded extraordinary results for such a large and rather mature region."
It comes after a year in which Spain has been gripped by the on-going dispute over Catalonia’s demand for an independence referendum, with protesters on both sides demonstrating across the country.
Barcelona also suffered a major terror attack when a van ploughed through pedestrians on the busy La Rambla shopping street, killing 14 and injuring over 100.
Overall, the number of international tourists rose by 7 per cent during the past year to 1.3bn. The growth is expected to continue in 2018.
"International travel continues to grow strongly, consolidating the tourism sector as a key driver in economic development," said UNWTO chief Zurab Pololikashvili.
"As the third export sector in the world, tourism is essential for job creation and the prosperity of communities around the world."
