Vienna police said on Saturday a "friendly" intelligence service had warned European capitals of the possibility of a shooting or bomb attack before New Year's, prompting police across the continent to increase security measures, NBC News reported.
"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.
Extra 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.
