Former deputy CIA director Mike Morrell on Thursday said he’s worried about the new threat of terrorists attacking airlines with shoe bombs.

“I am actually more worried about this threat than some of the other ones that we’ve talked about in recent weeks,” Morrell said on “CBS This Morning.”

“The fact that terrorists are coming back to shoes is also worrisome to me because it suggests that they may have found a way around the screening that is currently done on shoes, so that is a concern as well.” 

Morrell works as a contributor to CBS News. He resigned from the CIA last June, and had served as deputy director since 2010. 

DHS officials told The Hill the warnings to airlines about shoe bombs were based on new intelligence, but did not provide further details.

Al Qaeda factions in Pakistan and Yemen pose the largest threats now, Morrell said. Ibrahim Hassan Tali al-Asiri, for example, is al Qaeda’s top bomb-maker from Saudi Arabia, whom Morrell suspects might have discovered a way to evade airport security. 

“If he has found a way to be creative with shoe bombs, then that is something we need to worry about,” Morrell said. “So for example, he came up with this suicide vest that had no metallic parts so it would not show up on a metal detector. So I’m concerned that he may have found a way to put explosives in shoes that get around the current screening procedures.”

Flyers have been required to remove their shoes at airport security checkpoints since December 2001. The Transportation Security Administration introduced the rule after Richard Reid tried and failed to detonate a bomb on a flight that month.