Vienna police said on Saturday a "friendly" intelligence service has warned numerous European capitals of the possibility of a shooting or bomb attack before the New Year, pushing police across the continent to increase security measures.
"Several possible names of potential attackers were mentioned, which were checked, and the investigation based on (these checks) has so far yielded no concrete results," Vienna police said in a statement, some six weeks after 130 people were killed in Islamist bombing and shooting attacks in Paris.
"In the days before Christmas a warning was sent out by a friendly (intelligence) service to numerous European capitals, saying that it could come to an attack involving explosives or a shooting between Christmas and the New Year in crowded spaces," the statement said.
The tip also contained names of potential attackers. Authorities say that investigations those details hadn't yielded any credible results just yet.
Police spokesman Christoph Poelzl told the Austria Press Agency there was no concrete threat to a specific place at a particular time, and thus there is no need to call off any events.
The warning from the intelligence service, which the statement did not name, pointed to a higher threat level than "the general abstract" level cited earlier, Vienna police said, asking Austrians for their understanding for more controls.
Extra security steps include surveillance in crowded spaces, "especially at events and traffic hubs" as well as intensive identity checks and higher alertness for objects which could carry explosives such as bags or "bicycle frames", it said.
Vienna police were not immediately available for further comment.
A spokesman for the German Interior Ministry said it did not comment on particular situations for operational reasons.
"Germany is still in the crosshairs of Jihadist terrorism," he said, adding the country had reviewed and adapted its security measures, where necessary, following the Paris attacks.
French National Police refused to comment on the warnings when contacted by CNN, but did say that more than 48,000 police officers are dedicated to security at sensitive sites during the school holidays from December 19 through January 4, and France plans to recruit 2,000 new police officers next month.
A Belgian prosecutor who serves as a government spokesman on terrorism issues also refused to comment when contacted by CNN.
Bosnia: Attack in Sarajevo on Dec 31
Earlier this week police in Bosnia arrested 11 people in a wider Sarajevo area on suspicion of having planned terrorist activities and being connected with radical Islamist groups.
Those arrested planned to plant an explosive under a police car at a location where many people gather, Investigators have still not found the explosive, which was another reason why detention was requested, so the suspects could not destroy evidence.
- 22.12.2015 Bosnia: 11 arrested in Sarajevo on suspicion of links with ISIL
- 25.12.2015 Arrested radical Islamists planned terror attack in Sarajevo on Dec 31