Happy Thanksgiving? Terror, Not Turkey, Top Concern

Cities across the U.S. are on high alert this Thanksgiving week amid concerns of a potential holiday terror attack.

In New York, NYPD officers swarmed a subway station during a planned simulation of an active shooter underground.

"These exercises are vitally necessary in New York City; we are, at this time, very well prepared," NYPD Police Commissioner William Bratton said.

Security is especially tight at locations considered 'soft targets' – everyday places where large crowds gather like sporting events or shopping malls.

Over the weekend, Atlanta police received a tip from the hacker activist group Anonymous about a possible ISIS threat during a WWE event. Although nothing happened, Americans are on high alert.

Meanwhile in Europe, authorities continue their hunt for suspects from the Paris attacks.

Brussels, Belgium, is on the highest terror alert level for the third day in a row, with the threat of attack considered "imminent." The city is virtually on lockdown. Officials have closed schools and subway service has been suspended.

Meanwhile, the West is pulling together to support France and ramp up the war against the Islamic State.

British Prime Minister David Cameron says he will ask Parliament to approve allowing the British military to join in on the air strikes against ISIS in Syria.

"I firmly support the action President Hollande has taken to strike ISIL in Syria," Cameron said. "It is clear the world is coming together to tackle this terrorist threat."

This week, French President Francois Hollande will travel to both Washington, D.C., and Moscow to talk with President Barack Obama and Russian President Vladimir Putin about ways to fight back against ISIS.