Washington (AFP) - Republican presidential frontrunner Donald Trump says he sometimes carries a gun to protect himself, after a spate of shootings at colleges ramped up debate about firearms in the United States.

The revelation is likely to spark a backlash from advocates calling for tighter control of guns, after three separate shootings at US universities or colleges this month left 11 people dead.

Asked why years ago he obtained a concealed weapons permit, Trump told the CBS program "Face the Nation": "Because I like to have myself protected."

Host John Dickerson then asked Trump: "Do you carry?"

"Sometimes," replied Trump, whose popularity has surged on the back of a series of bombastic comments on a range of sensitive topics, including immigration and gun control.

Last week, days after a gunman shot dead nine people at a college in Oregon on October 1, Trump said that gun laws had "nothing to do" with the spate of shootings and that such incidents were simply a fact of life.

The mass shooting at the community college in Roseburg was "horrible," Trump told CBS.

"Had somebody in that room had a gun, the result would've been better," he said, adding that "I feel much better being armed."