NEW YORK (CBSNewYork/AP) — Just days before the start of the holiday season, many people have expressed concern after a U.S. State Department warning that said Americans should be alert for possible travel risks following increased terrorist threats around the world.

A new intelligence bulletin sent to law enforcement around the country also said there may be copycats in the U.S. looking to replicate the Nov. 13 Paris attacks.

The travel alert, which is to be in effect until Feb. 24, said current information suggests that militants with the Islamic State, al-Qaeda, Boko Haram and other terrorist groups continue to plan attacks in multiple regions.

U.S. authorities said the likelihood of terror attacks will continue as members of ISIS return from Syria and Iraq, and other individuals not affiliated with terror groups engage in violence on their own.

“U.S. citizens should exercise vigilance when in public places or using transportation,” the alert said. “Be aware of immediate surroundings and avoid large crowds or crowded places. Exercise particular caution during the holiday season and at holiday festivals or events.”

Officials urged that when traveling, you should follow the instructions of local officials, expect additional security screening, stay in touch with family so they know how to contact you, and register with STEP – the Smart Traveler Enrollment Program that provides assistance in emergency while traveling abroad.

Security experts say the warning means something on a large scale is likely going to happen, so be alert.

“I would be concerned,” said terrorism expert Manny Gomez. “Obviously, they have some information leading them to believe there will be an attack. The problem is they don’t know where, how or when.”

The increased security measures follow the Nov. 13 attacks in Paris that killed 130 people and have virtually shut down the Belgian capital.

Extremists have targeted sporting events, theaters, open markets and aviation targets. In the past year, there have been multiple attacks in France, Nigeria, Denmark, Lebanon, Turkey and Mali. IS has also claimed responsibility for the Oct. 31 bombing of a Russian airliner in Egypt, killing 224 people.

The State Department said the U.S. is exchanging information with allies about threats of international terrorism.

Meanwhile, the concern about terror in the homeland is so high that President Barack Obama urged Americans not to “succumb to fear.”

“For that’s how terrorists win,” Obama said. “We cannot give them the victory of changing how we go about living our lives.

As CBS2’s Dick Brennan reported, back in New York, police Commissioner Bill Bratton said the NYPD is doing everything to make people safe during the holidays, and he encouraged people to come out to the Macy’s Thanksgiving Day Parade on Thursday.

The balloon blow-up on the Upper West Side was under way for the parade on Tuesday, in one of the kick-off events of the holiday season. The NYPD said it is ready, rolling out its counterterrorism overlay for major holiday events.

That includes extra uniformed police officers and traffic agents, mobile cameras, helicopters, mounted units, observation posts manned by the Emergency Service Unit, plainclothes officers, specially-trained dogs, and radiation detectors.

“This year, for the first time, our force will be supplemented by approximately 200 freshly-trained armed critical response command cops, working along with our police officers from the Strategic Response Group,” said NYPD Chief of Department James O’Neill. “There will be a lot of police presence — things the public will see, and of course, things the public will not see.”

But look anywhere these days and you cannot miss a massive police presence around town, and that will be even more noticeable at the Thanksgiving Day parade.

“Some of those officers will be equipped with the long guns, as we refer to them; the rifles. We’ll have additional Hercules teams – those are the heavily-armed entities that will be around the area of the parade route,” Bratton said. “But I think the police presence will heighten the sense of security.”

As CBS2’s Tony Aiello reported, it may have felt for some as if a cloud of anxiety was hanging over the star of the holiday season with the extra security. But others felt better with the additional officers in place.

“They’re everywhere! I like that – I love that,” said Terri Butler of the Lower East Side. “That’s very important. We need that here in the city.”

“Whenever you’re in large crowds, this is places like where they’d target,” said Heather Walker of Harlem. “But I don’t really worry about it. You can’t live in fear.”

Meanwhile, passengers at LaGuardia Airport tried to play it cool following the State Department alert. But many expressed worries anyway.

“It’s definitely stressful,” said Lauren Hoffman.

“I have to travel for work, so I don’t have much of a choice,” added a man named Kurt.

The FBI and the Department of Homeland Security also warned local police forces about new tactics by ISIS. Bratton said New Yorkers should be aware, but not afraid to enjoy holiday events.

“And if there is something that they see that makes them feel uncomfortable, certainly make us aware of it. We can very quickly check it out with the very large numbers of personnel that we have there,” Bratton said.

Meanwhile, CBS News has also learned the FBI and the Department of Homeland Security sent out a joint intelligence bulletin to law enforcement across the United States warning them of ISIS’ new tactics.

Agencies across the country have been retraining officers in active shooting drills – including one in a Lower Manhattan subway station this past weekend.

“We have been concerned about copycat-like attacks,” said Secretary of Homeland Security Jeh Johnson.

While federal law enforcement officials have emphasized there is no specific or credible threat to the U.S., security has also been heightened at airports and other locations, CBS News reported.

And elsewhere in the world, it was even more intense. There was not much holiday cheer in Brussels, which was virtually shut down against an imminent threat of a serious terrorist attack.

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