Could Kenya terror attack be first in wave of strikes?

(CBS News) Just days after the Nairobi attack, there is a renewed global terrorism alert. The State Department issued what it calls a "worldwide caution." Americans are warned they could be targeted not only in Africa, but Asia, Europe and the Middle East.

The alert may be tied to the attack in Kenya "in some ways," according to CBS News senior correspondent John Miller, a former FBI assistant director, but there is a larger issue that may be driving the heightened awareness.

Miller said on "CBS This Morning," "The larger thing that's driving it is back in August the intelligence community received information that my sources described to me as the most specific and the most serious threat information they'd received since the British planes plot in 2006. And they said, 'We know the threat, we know there's an operation going. We don't know where it's going to be or when. We know it's in the works.'"

He continued, "So the question is was this Kenya thing it? That's doubtful. The question is was this the first in a wave of possible attacks, and that's what they're concerned about."

In the wake of the Nairobi mall attack, the Mall of America in Minneapolis has ramped up security.

Minnesota is home to the largest Somali community in the U.S. The Associated Press reports at least 22 young men have traveled to Somalia since 2007 to join al-Shabab and the FBI says its investigation of the terror group's recruiting remains a priority. FBI spokesman Kyle Loven says there's no confirmation of any American involvement in the Nairobi attack that the Kenyan government says has killed at least 61 civilians.

Miller said malls are "a real concern" following this attack. He said, "Malls across the country and the world who are saying, 'Do we have the right plan for an active-shooter situation or more?'"

Two dozen FBI agents are assisting with the investigation at the Nairobi mall. Miller said the help is due to a relationship between the FBI and the government and counterterrorism forces in Kenya forged following the U.S. Embassy bombings in Kenya and Tanzania in 1998. "This is what you'd expect to see here," Miller said. "They want to use the FBI's forensic ability, and the FBI is very interested to see, are there Americans among the terrorists."

Watch the full discussion with John Miller in the player above