There has been much talk about whether or not European countries and the United States should accept more refugees from war-torn areas in the Middle East, primarily due to fears that some of them may be covert terrorists.

It turns out those security fears are well-founded, based on recent pronouncements made by the Supreme Allied Commander of the North Atlantic Treaty Organisation (NATO).

In his testimony to the Senate armed services committee earlier this week, NATO Supreme Allied Commander and U.S. Air Force Gen. Philip Breedlove warned that migrant populations from the Middle East and north Africa are "masking the movement" of terrorists and criminals.

The ranking military official even went as far as saying that the jihadist organisation Islamic State (ISIS) is "spreading like a cancer" among refugees.

He further warned that the ISIS is already "threatening European nations and our own" by "taking advantage of paths of least resistance," which was through strengthening its force in migrant populations.

Breedlove likewise accused Russia of "wildly" exacerbating the problem by unilaterally launching a bombing campaign in Syria, in support of the war-torn nation's autocratic leader, Bashar al-Assad.

The NATO commander said Russia's airstrikes in Syria, which has already killed some 1,000 people including children, are forcing more people from the Middle Eastern country to flee for their lives and try to find refuge in Europe no matter how difficult and perilous that may be.

Asked by the media if he has data to support the claims he made before Congress, Breedlove just replied: "I can't give you a number on the estimate of the flow."

"I'm not going to talk to you about intelligence," he further said, warning that "many [countries] are saying they see planning happening" for a terrorist attack.