An undercover Muslim FBI operative opened up in an interview on Sunday about his experience working in terror cells in an effort to relay information to the bureau, saying he is "appalled" by the "animals" working to attack the U.S.

"We're not at war with Islam. We’re at war with radicals. I am a Muslim. I am an American. And I've been serving my country for 22 years and counting. And I am appalled at what these animals are doing to my country while desecrating my religion," Tamer Elnoury, which is one of operative's aliases, told CBS's Scott Pelley on "60 Minutes." 

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Elnoury went on to talk about his work infiltrating cells in the U.S., one of which involved targeting Tunisian Chiheb Esseghaier, who was getting his PhD at a Canadian university while working with al Qaeda.

Esseghaier had planned a terror attack on a Toronto-bound train from New York City, and mulled a potential New Year's Eve attack on Times Square, a sign that the group's attack strategies had changed since the Sept. 11, 2001, attacks. 

"Chiheb said that al Qaeda shifted gears. After 9/11, they lost some of their best minds. No more martyrdom. It was maximum casualties, minimum exposure. That was their mindset. And they didn't wanna lose soldiers anymore, people with access to the West. So you do what you can and get out, hide, and do it again," Elnoury said. 

Chiheb and an accomplice were arrested and sentenced to life in prison in 2013, although he had mentioned the existence of an American sleeper working for the organization who has not been found. 

"There hasn't been a day since April 22nd, 2013 when I've woken up, no matter where I am, that I don't think about the American sleeper," Elnoury said.