A recently retired senior CIA official calls Syria's ongoing civil war the No. 1 threat to U.S. national security due to an increasing al-Qaida presence.

"It's probably the most important issue in the world today because of where it is currently heading," Michael Morell, who announced his retirement as CIA's deputy director in June, told the Wall Street Journal. He predicted President Bashar al-Assad's government ultimately will fall. Other threats Morrell listed included Iran, al-Qaida, North Korea, and cyberwarfare.

The Syrian crisis is similar to the situation prevailing in Libya leading up to the fall of the Muammar Gaddafi regime, Morell said. Weapons now controlled by the Syrian government "are going to be up for grabs and up for sale" like they were in Libya.

Morrell's remarks reflect the dilemma faced by U.S. policymakers as they seek to arm Syrian rebels fighting the brutal Assad regime that has reportedly used chemical weapons to squash the rebellion. Policymakers fear the arms supplied to Syrian rebels might fall into the hands of terrorists fighting on the side of the rebels, including the al Nusrah Front, al-Qaida's affiliate in Syria.

According to a recent ProPublica report, the Syrian conflict also has emerged as a top security threat for Europe. "The global jihad has prioritized the Syrian conflict as its principal front," an unnamed senior Spanish intelligence official told the news outlet. It has served as a magnet for hundreds of Europeans and thousands of Sunni Muslim fighters wanting to wage jihad.

There is concern that Europeans radicalized in the Syrian conflict could bring their jihad home, or potentially attempt to attack U.S. targets.