The Department of Homeland Security and the FBI sent a bulletin to local U.S. law enforcement agencies Sunday morning, saying there was currently no information about specific threats to U.S. targets, but they are monitoring recent terrorist threat reports regarding Europe and would continue to "assess."
The bulletin noted al Qaeda affiliates and those who "follow their ideology" may inspire those with "the ability to access the U.S. legally" and expressed concerns about possible attacks using "small arms, lone shooters and small unit tactics."
Federal authorities urged localities to raise general security awareness, including training private security staff to take note of individuals "loitering for no apparent reason, sketching or pace counting."
In a phone conference with reporters Sunday, State Department officials took pains not to discourage travel to Europe with the alert and gave few concrete steps to take.
"Use common sense," said State Department Undersecretary Patrick Kennedy. "If [tourists] see unattended packages or hear loud noises, quickly move away from them."
Authorities have detected a dramatic increase in online chatter among jihadist websites the last week, in what experts believe could be other terrorists banning together in anticipation of terror attack plans in Europe and hoping to engage themselves in prospective plots.
The escalating discussions in the virtual meeting rooms for al Qaeda supporters have praised terror attacks plan and suggested targets, communicating with fellow believers just as the terrorist teams at the center of the current suspected plots likely did, experts said.
"When you've got this set of threats, what you're really seeing is the culmination of online chatter a couple years ago," said jihadi website monitor Aaron Weisburd, an instructor at West Point's Combating Terrorism Center. "These are the guys who represent a real threat right now."
There's real significance to chatter when combined with other elements of intelligence, said Garrett.
"The government's already saying publicly that they are concerned with this level of chatter and they're concerned about U.S. interests in Europe," Garrett said. "I think that makes it particularly important."