Austrian police said Saturday they stepped up security in Vienna and other cities after receiving a warning of possible attacks during the holiday season.
"In the lead-up to Christmas, a friendly intelligence service sent a warning to numerous European capitals saying potential bomb or gun attacks could take place in areas with large crowds between Christmas and New Year," Vienna police said in a statement.
The warning included "several names of potential attackers" but investigations have so far yielded no concrete results, the statement said.
In response to the alert, police officials said they would increase security at public events and tighten controls on roads in Vienna and elsewhere in Austria.
The warning comes after jihadist gunmen and suicide bombers killed 130 people in a series of coordinated attacks in Paris on November 13.