Speaking at a news conference Friday, Munich police chief Hubertus Andrae said the decision to temporarily shut down two major railway stations in the city was taken after German officials received a “very concrete” tip that militants from Iraq and Syria were planning suicide attacks in the area at midnight. While the stations have since reopened, Munich police are still on high alert and are carrying out more security checks that usual.

“We received names. We can't say if they are in Munich or in fact in Germany,” Andrae reportedly said, when asked about the suspects’ whereabouts. Earlier Friday, German authorities had confirmed that up to seven people were part of the plot to carry out suicide bombings at the city’s main Hauptbahnhof and Pasing station.

Nearly 550 police officers have been deployed to hunt down the suspects, according to media reports

The alert came just hours before midnight and police in the Bavarian capital warned people to avoid crowds. Police evacuated the two train stations over an hour before New Year celebrations began in Munich.

“The Federal Criminal Police Office informed the Bavarian police on New Year’s Eve of the existence of a tip-off from a friendly intelligence agency that Islamic State plans a concrete attack,” Bavarian Interior Minister Joachim Herrman reportedly said, at a news conference earlier Friday, without naming the intelligence agency.

“I believe this decision [to evacuate the stations] was right because I think we cannot take unnecessary risks when we are dealing with such concrete threats, concrete locations, and a concrete time,” he added.

High-profile attacks claimed by ISIS and other groups have cast a shadow over New Year’s Eve celebrations around the world. A planned fireworks display in Brussels, Belgium, was canceled Wednesday night over fears of an attack. Belgian police said late Thursday that three people were being held for questioning as part of an investigation into an alleged plot.

The terror threat in Munich capped one of the deadliest years of militant violence in Europe. Additionally, following November’s deadly attacks in Paris, claimed by ISIS, anxieties over a rapidly burgeoning refugee crisis have also gripped Europe, leading to a rise in popularity of several right-wing, anti-immigration political parties.