"Would you go look for them, though?" O'Reilly then asked, noting that Donald Trump has said he would "look for them" and conduct mass deportations.

"Bill, of course you would, that's what ICE exists for. We have law enforcement that looks for people who are violating the laws, that apprehends them and deports them," Cruz replied.

O’Reilly then described a fictional undocumented Irish immigrant who has overstayed his visa and asked, "And you, President Cruz, are going to send the feds to his house, take him out, and put him on a plane back to Ireland?"

"You better believe it," Cruz said in response.

Cruz later added, "Both Donald Trump and Marco Rubio would allow those 12 million people to become U.S. citizens. I will not."

Cruz's Monday night comments mark an escalation in the way he discusses deportation of undocumented immigrants. In a January interview on CNN, Jake Tapper noted that Trump has said he would create a "deportation force" and asked whether Cruz would go door-to-door to round up undocumented immigrants.

"No, I don't intend to send jackboots to knock on your door and every door in America. That's not how we enforce the law for any crime," Cruz said at the time.

Watch the Monday interview via Fox News. O'Reilly asks about immigration near the 2:30 mark.