Police, military forces in many cities around the world placed on alert

Europe ushered in the New Year with heightened security fears on Friday as German police evacuated two train stations in Munich, citing a tip about a planned suicide bomb attack, and Belgium held three people over an alleged plot.

Security forces in many capitals were on raised alert after a year of militant attacks, including an attack in Paris in November that killed 130 and was claimed by Islamic State.

Soldiers were on the streets of the French capital, and police forces in London, Madrid, Berlin and Istanbul increased their presence as Europeans turned out to celebrate the arrival of 2016.

In New York, police tightened security for the traditional New Year's Eve dropping of the crystal ball in Times Square, where more than 1 million people had gathered.

Celebrations in Germany took on a somber note when police warned of a possible terror attack and evacuated two train stations in Munich an hour before midnight on Thursday.

Germany had received a tip from another country's intelligence service that IS planned to attack Munich with up to seven suicide bombers, German officials said at a news conference on Friday.

They didn't identify the country that provided the tip-off, but German television said in an unsourced report that it came from France.

"I believe this decision was right because I think we cannot take unnecessary risks when we are dealing with such concrete threats, concrete locations, and a concrete time," Bavarian Interior Minister Joachim Herrmann told a news conference on Friday.

The stations - Munich's central station and Pasing station some 8 km away - reopened several hours later after the threat could not be substantiated.

In Belgium, police were holding three people for questioning on Thursday as part of an investigation into an alleged plot to carry out an attack in Brussels on New Year's Eve.

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

Police had initially detained six people after searches at six locations in the Belgian capital and one just outside the city. They also seized computers, mobile phones and equipment for airsoft, a sport using guns that shoot nonlethal plastic pellets.

Three of the six were released late on Thursday. Prosecutors said they were holding the other three for a further 24 hours.

French President Francois Hollande said on Thursday the country was "not finished with terrorism" and used a New Year's message to defend controversial plans to strip citizenship from those convicted of terrorism offenses.

"The threat is still there," he said in a televised address. "It remains in fact at its highest level, and we are regularly disrupting planned attacks."

In Istanbul, a bridge between the continents of Europe and Asia, police said they had ramped up the number of officers on the streets by around 10,000.

Turkish police on Wednesday detained two suspected Islamic State members they believe to have been plotting New Year's Eve suicide attacks in the capital Ankara, where less than three months ago a double suicide bombing killed more than 100 people.

Last year was the deadliest year of militant attacks in Europe since 2004. Evidence that two of the Nov. 13 Paris attackers had entered the continent under cover of a wave of Middle Eastern refugees heightened anxieties over the migration crisis.