How serious is July 4th terrorism threat?

The FBI and Department of Homeland Security are warning people to 'remain vigilant' at Independence Day events following a series of deadly attacks by the Islamic State last week. 

Federal authorities are warning law enforcement officials across the country to remain vigilant throughout the week of July 4th as concern about potential terror attacks grows. 

An intelligence bulletin issued Friday by the Department of Homeland Security and the FBI urged local authorities to keep in mind the ongoing threats posed by the Islamic State and other homegrown extremists. 

While there is currently no specific or credible threat of attack, House Homeland Security chairman Michael McCaul said on Fox News Sunday the confluence of the Islamic holy month of Ramadan, the one-year anniversary of the creation of the Islamic State, and America's Independence Day weekend are cause for concern. 

Former CIA deputy director Michael Morrell told CBS News that while similar warnings are issued every year, "there's nothing routine about this particular one to me."

"I wouldn't be surprised if we're sitting here a week from today talking about an attack over the weekend in the United States. That's how serious this is," Morell said. 

Rep. Peter King (R) of New York echoed the same concerns in an interview with ABC News, saying that "there's probably more concern now than any time since September 11." 

The warnings come following three deadly terror attacks France, Kuwait, and Tunisia last week. In southeastern France, a man attempted to blow up an American-owned chemical plant and decapitated a person on Friday. In Kuwait City, a suicide bombing in one of the largest Shiite mosques in the area killed at least 27 people. In Sousse, Tunisia, 38 people were killed when gunmen opened fire at a beach resort. 

The attacks came shortly after ISIS spokesman Abu Mohammad al-Adnani called on Islamists to take action during the month of Ramadan. 

"O mujahidin everywhere, rush and move to make Ramadan a month of disaster," he said Tuesday, encouraging supporters to "embark and hasten towards jihad." ISIS has taken credit for the massacres in Kuwait and Tunisia. 

These tragic events demonstrated that the organization is a "global threat" and that "they're very savvy" at recruiting followers and coordinating acts of terror via the internet, McCaul says. He is "extremely concerned" about ISIS recruiters who can "use the Internet at lightning speeds to recruit followers in the United States" and then "activate them to do whatever they want to do." 

Earlier this month, two college students from New York were charged with conspiring to support a foreign terrorist organization after an investigation found that they were planning to attack various New York City landmarks on behalf of ISIS. Their arrests came roughly two weeks after a Muslim man in Boston was shot and killed by members of a terrorism task force when he allegedly approached law enforcement officials brandishing a large knife. 

It's unknown exactly how many Americans have been caught trying to join or help ISIS, but at least 180 have attempted to go fight in Syria, said National Intelligence Director James Clapper in March. Especially vulnerable to this recruitment are socially isolated young people.

Homeland Security Secretary Jeh Johnson encourages people to attend Fourth of July celebrations as planned this weekend, but to "remain vigilant" and report any suspicious activity.