U.S. officials have seen an uptick in terrorist chatter over the past several months as the 15th anniversary of the Sept. 11, 2001, attacks approaches, raising fears that a lone wolf or cell might strike during ceremonies commemorating one of America's darkest days.
And they warn it may be an observant citizen -- and not police -- who preempts the next attack since the intelligence community is increasingly blinded by the encryption technology being used by Islamist groups and their supporters to communicate.
The uptick in chatter within terror groups is not uncommon as the anniversary approaches, law enforcement officials say.
The FBI told Circa that while there is no specific or credible threat to the United States, it is asking "members of the public to maintain awareness of their surroundings and to report any suspicious activity to law enforcement immediately."
But the situation is becoming more precarious, law enforcement and intelligence officials say.
Al Qaeda, the Islamic State and their off-shoots have found ways to adapt to Western counterterrorism measures, persuade lone wolf attackers to hit less guarded targets and utilize technology to evade intelligence personnel from monitoring chatrooms on the internet.
Last week, the Department of Homeland Security issued a warning to law enforcement that terrorists aligned with Islamic State "may be inspired or directed to conduct attacks against events associated with 9/11 memorial commemorations."
Cities across America will be commemorating the 15th anniversary of the Sept. 11 attacks on Sunday.
Tracking the terrorist threat is getting more difficult, officials say.
"Terrorist actors are communicating with each other outside our reach with the use of encrypted communications," said a U.S. counterterrorism official with direct knowledge of the ongoing threats. "We have also seen a decrease in the frequency of large scale, complex plotting efforts in favor of more rapidly evolving threats or plot vectors, which has led to a compression in the time between when an individual decides to attack and when the attack occurs."
A U.S. military official, who works in the Middle East and South Asia, told Circa that 15 years after invading Afghanistan to rout Al Qaeda for attacking the World Trade Center and Pentagon, that country is once again becoming a safe haven for anti-American terrorists.
"We're worse off than we were before, and we're not paying attention to how dangerous it is," the military official said. "Al Qaeda is back, ISIS is here now and the Taliban are growing in strength." He noted that chatter is up as well.
A Taliban video obtained by Circa shows extremist fighters showing off a cache of weapons, uniforms and vehicles captured from Afghan security forces.
Kim Jensen, a retired counterterrorism instructor with the FBI and an expert on terror groups in the Middle East, said holidays and anniversaries play an important role for terror organizations. He said the expansion of Islamic State has made the the world "more dangerous now than before Sept. 11."
"When you think how group's like Islamic State have grown exponentially it shouldn't be surprising," he added. Jensen warned the failure of government organizations to fully understand what defines these terrorist groups has allowed them to expand.
It's almost like fighting a ghost.
"You have to undermine the extremist ideology," Jensen said. "The only way to undermine it, is to understand it completely. It's impossible to defeat something you can not even define. It's almost like fighting a ghost. When you can define it, you can address it."
Just last week, Malaysian authorities narrowly stopped ISIS followers from attacking on the nation's 59th independence day.
Authorities, who arrested three suspected ISIS terrorists, said the group was planning multiple attacks in the country's capital of Kuala Lumpur.
Federal and local law enforcement officials admit the difficulty is trying to stop the attacks and keep track of all the individuals suspected of being terrorists or connected to terrorist organizations.
The Orlando nightclub shooting, San Bernardino shooting, random knife attacks in Germany, the attacks at the Bataclan Cafe and restaurants in Paris and the truck attack in Nice, France are some examples of the difficulty law enforcement and intelligence officials have in connecting the dots.
In fact, last year FBI Director James Comey revealed his agency was investigating suspected Islamic State supporters in 50 states and admitted it was "highly unlikely" that it would be federal agents that would first discover someone acting strangely.
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