Vienna police stepped up armed patrols at sensitive sites in the Austrian capital including churches on Wednesday after the country's domestic intelligence agency received information suggesting an Islamist attack was being planned.
The city's police took the rare step of warning the public on social media that there would be a heightened presence of armed police, including special forces, in the city.
Vienna is among the safest capitals in the world and militant attacks are rare. The first deadly attack in a generation took place in 2020 when a jihadist gunman killed four people in a shooting rampage before being shot dead by police.
"Our intelligence services have reason to believe that an assault with an Islamist motive is planned to be carried out in Vienna," Vienna police said in English on Twitter.
"As precautionary measure... points of interest have been put under increased guard by regular & special operation police forces," the police said, adding that it was not possible to say how long the special measures would last.
How did the concern for attacks in Vienna impact city visitors?
The tourist-filled streets of central Vienna were busy as usual after the police warning. The increased police presence at the city's St Stephen's Cathedral was barely noticeable.
More than three hours after its tweets alerting the public to the possible threat, the police sent just one update to clarify that an initial reference to a risk of an attack against churches in fact meant not only Christian churches but various religions' places of worship and other buildings.
The police did not elaborate but said the special measures remained in place.