A tip-off hours before new year celebrations in Munich named militants from Iraq and Syria who were planning attacks, but police have been unable to find the suspects and are not even sure if they exist or are in the country, German authorities say.

Key points: Militants from Iraq and Syria were reportedly planning attacks in Munich

Militants from Iraq and Syria were reportedly planning attacks in Munich French intelligence says Islamic State was behind the planned attacks

French intelligence says Islamic State was behind the planned attacks But authorities unsure if the suspects exist or are in the country

But authorities unsure if the suspects exist or are in the country Warning comes amid concerns about terrorist threats across Europe

Munich police chief Hubertus Andrae said officials had received a "very concrete" tip that suicide attacks were planned for New Year's Eve at two train stations.

Police closed the stations about an hour before midnight, and reopened them hours later.

"We received names. We can't say if they are in Munich or in fact in Germany," Mr Andrae said.

"At this point we don't know if these names are correct, if these people even exist, or where they might be.

"It was not a false alarm — it was information and we have to do our job and we have to investigate this and we have to guarantee the security and the safety for our people here in Munich."

Bavaria Interior Minister Joachim Herrmann said the tip, which media reports said came from French intelligence, indicated that the Islamic State (IS) militant group was behind the planned attacks.

The shutting down of the stations added to jitters in many capitals as Europe ushered in the New Year with heightened security after a year of militant attacks, the deadliest of which killed 130 in Paris in November.

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German police lifted an alert of an imminent attack in Munich, hours after two key train stations were evacuated.

"Overall I would say that the situation for Munich is as it was before this threat of attack," Mr Andrae said.

In a security update, Munich police also issued a statement saying that "following investigations, there is currently no concrete risk of an attack" in the city.

On their Twitter feed, Munich police said: "Good morning to those, who spent the night out in #munich! Thanks for staying calm and for your understanding concerning our measures."

Police said they had received information that five to seven suicide bombers were planning to take part in the attack.

The Munich alarm followed days of security warnings in Europe.

On December 26, police in the Austrian capital Vienna said a "friendly" intelligence service had warned European capitals of the possibility of a shooting or bomb attack before the new year.

That tip, too, had included the names of several suspects.

In Belgium, authorities on Wednesday called off the usual New Year's Eve fireworks display in the capital, citing fears of a possible militant attack.

Police said on Thursday they were holding three people for questioning over an alleged plot.

The US Justice Department said on Thursday that a 25-year-old man accused of planning to attack a restaurant in upstate New York on New Year's Eve had been arrested and charged with attempting to provide material support to IS.

Reuters