Planning to go to Europe in the coming months? You better reconsider your travel plans, because the threat of terrorism in the continent is real.

A counterterrorism expert advised residents in the United States to take the American government's travel warnings against Europe seriously, knowing how terrorists are known to keep their word on their evil plans.

"Every time they have declared their intentions, they've followed through," Philip Haney, a founding member of the U.S. Department of Homeland Security told WND.

He also urged European authorities to seriously be on the lookout for movements of terrorist groups like those affiliated with the jihadist organisation Islamic State (ISIS).

"You have to assume they mean exactly what they say. With the threat level we see, the primary responsibility of the police and of those working in national security is to accept that, take that threat seriously and protect the general public from that threat," the counterterrorism expert said.

The U.S. State Department recently warned residents against travelling to Europe this summer, citing "risk of potential terrorist attacks throughout Europe, targeting major events, tourist sites, restaurants, commercial centres and transportation."

The government agency particularly warned Americans against participating in the European Soccer Championship, which is scheduled for June 10 through July 10 in 10 different stadia across France.

Americans were also told not to join the World Youth Day event for Roman Catholics in Krakow, Poland beginning July 25.

Haney, a highly decorated Customs and Border Protection officer who was able to identify hundreds of terrorists throughout his career, said the ISIS usually goes for widescale and spectacular terror attacks—a good reason to heed the U.S. State Department's warning against joining these mass events.

"It's the larger level attacks the authorities are concerned with," Haney explained. "And they know from intelligence they gathered after the last attacks that there was an extensive amount of planning going on before the previous wave. And even some of the terrorists they captured said there were going to be other attacks."

He also opined that Islamist extremist groups like the ISIS pose not only a security threat to the U.S. but an ideological threat as well.

"It's not a matter of First Amendment free speech and exercise of religion," Haney said. "It's actually an Article VI issue. Article VI of the Constitution says that the Constitution will be the supreme law of the land. Whereas with Shariah, it would supercede the Constitution. Right there, on that simple basis, taking religion completely out of it, any other system of law that seeks to impose itself on our constitutional form of law should be prohibited."