The US Air Force views Russia as the greatest challenge to US national security, even when compared to Islamic State (IS, formerly ISIS/ISIL) and North Korea's nuclear ambitions.

“I think the number one threat is Russia. [Russia] is one of the handful of [countries] that could actually present an existential threat to the US,” US Air Force Secretary Deborah Lee James told Fox News' 'America's News HQ' program.

“They have nuclear weapons. They have been acting [in] very aggressive manners in recent years. And they are also investing and are testing military capabilities...that is very worrisome for the United States and to our allies,” she elaborated.

Claiming that the US Air Force is “now globally engaged to deter and to counter” a number of threats, James went on to list them.

“We are facing resurging Russia in Europe and in other parts of the world. We now have a fight against this group called ISIL that did not exist a few short years ago.”

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“We have issues in the South China Sea. We have N. Korea that is investing and testing and acting in a very belligerent way,” James said, placing Russia at the top of the list.

This is not the first time that American politicians and top military brass have called Russia the greatest threat to the United States, particularly during the two years following the outbreak of the Ukrainian conflict in 2014.

In late July, NATO Supreme Allied Commander Europe (SACEUR) General Curtis Scaparotti of the, who also serves as head of US European Command, said he was “impressed” by Russia’s efforts to modernize its military.

“They’ve been watching us...they’ve fired long-range precision missiles from submarines, from surface ships, from medium bombers, all at Syria,” he said.

“You know, we have an adversary here that we have to take very seriously.”

US Defense Secretary Ash Carter told the Washington-based Center for Strategic and International Studies in April that America faces five strategic challenges, which he named as “Russia, China, North Korea, Iran, and terrorism.”

In turn, Russia’s military leaders linked stirring up fears of the so-called "Russian threat" to the US military’s struggle for a defense budget worth $582.7 billion.

“One needs to remember that the ‘Russian threat’ has been the best-selling threat delivered by the Pentagon not only to Congress, but also to NATO partners since the middle of the previous century,” Russian Defense Ministry spokesman Igor Konashenkov said in February.