Republican presidential candidate Ben Carson said on Sunday that Muslims are unfit to be president of the United States, arguing their faith was inconsistent with American principles.

"I would not advocate that we put a Muslim in charge of this nation. I absolutely would not agree with that," Carson told NBC's "Meet the Press."

Carson, a Christian who says he got the idea for his tax proposals from the Bible, said he thought a U.S. president's faith should be "consistent with the Constitution."

Asked if he thought Islam met this bar, the retired neurosurgeon said: "No, I do not."

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America's largest Muslim civil rights group condemned Carson for his statement, which it said should disqualify him from the presidential contest because the U.S. Constitution forbids religious tests for holding public office.

"It's beyond the pale, and he should withdraw," said Council on American-Islamic Relations spokesman Ibrahim Hooper.

In a statement later on Sunday, Carson campaign spokesman Doug Watts said, "Without question, there are complex differences between the practice of the Muslim faith and our Constitution, differences that are very real and very much in conflict with one another.”

Carson's comments drew scorn from Republican Sen. Lindsey Graham, another presidential candidate, who said, "I think Dr. Carson needs to apologize,” adding the comments were offensive to U.S. soldiers who are Muslim.

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Carson recently gave up some ground in a CNN/ORC poll released on Sunday, slipping to third place with 14 percent supporting his candidacy. The poll showed that Trump continued to lead with the support of 24 percent of registered voters, down from 32 percent in a previous poll, with former Hewlett-Packard Chief Executive Officer Carly Fiorina surging into second place with 15 percent.