A “friendly” intelligence service has warned several European capitals of the possibility of fresh terror attacks being carried out before the New Year, in the form of shooting or bomb attacks, police in Austria have said.

The European capitals have not been named, but security measures in Vienna have been increased after the city’s police service said the warning had detailed a possibility of an attack between Christmas and the New Year, and could be expected to take place in “crowded places”.

“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.

“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.”

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France remains under a state of emergency following the attacks in Paris in which 130 people were brutally murdered by terrorists in Paris six weeks ago.

Vienna police have asked Austrians for their understanding as security controls are increased, including surveillance in crowded places “especially at events and traffic hubs,” in addition to intensive identity checks and a higher alertness for objects that could carry explosives, such as bags or “bicycle frames,” but no specific events will be cancelled.

Christph Polzl, a spokesman for the police service, said: “We do not know if these people exist in real life, or if they are only names with no real person behind them.

“We have no evidence they are in Vienna, and we have no evidence that they are even in Europe,” he said, the Guardian reported.

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.