Police in Vienna are ramping up security after receiving a tip that raised the possibility of an attack on numerous European capitals using guns and explosives between Christmas and New Year's Eve.
In a statement on Saturday, the Viennese Police said the warning, which they received in the days before Christmas, came from an "unidentified friendly" intelligence service. Authorities wouldn't say which other European capitals were included in the warning.
The tip also contained names of potential attackers. Authorities say that investigations into those details hadn't yielded any credible results just yet.
"We do not know if these people exist in real life or if they are only names with no real person behind them " Christoph Pölzl, a spokesman for the Vienna police, told the Guardian. "We have no evidence they are in Vienna, and we have no evidence they are even in Europe."
Upcoming events in the Austrian capital will go ahead as planned, police say, but added that they plan to step up surveillance of areas likely to draw crowds, such as transport hubs. They will also keep a closer eye on any suspicious bags or suitcases.
Ever since coordinated attacks claimed by the Islamic State killed 130 people in Paris on November 13, fears of subsequent attacks in Europe this holiday season have authorities on high alert. Last week, France's interior minister, Bernard Cazeneuve, urged police and security forces to be especially vigilant at holiday church services. Police presence was also noticeably heavier across French and German Christmas markets, where people traditionally gather to shop and drink mulled wine.