Albuquerque, New Mexico (CNN) Donald Trump on Sunday warned his supporters in this border state that Hillary Clinton "wants to let people just pour in," saying without evidence that hundreds of millions of people could enter the US under a Clinton presidency.

And speaking just nine days before Election Day, the Republican nominee also bemoaned criticism of waterboarding and appeared to once again call for bringing back the since-banned technique for use in the fight against ISIS.

"These savages are chopping off heads, drowning people. This is medieval times and then we can't do waterboarding? 'It's far too tough,'" Trump said, mocking critics of the technique used by the CIA in interrogations of terror suspects under President George W. Bush's post-9/11 administration.

Trump has previously called for reinstating waterboarding and "much worse" methods of torture if he becomes president.

"We have to be tough and we have to be smart. And we have to be in some cases pretty vicious I have to tell you," he added.

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