Story highlights "You know they haven't been able to define waterboarding. They don't know if it's torture," Trump said

Trump has previously referred to waterboarding as "sort of the least form of torture"

(CNN) Donald Trump still isn't sure if waterboarding amounts to torture.

Despite previously acknowledging that the controversial technique is torture, the GOP front-runner appeared to backtrack on Thursday, saying that "nobody knows if it's torture."

"You know they haven't been able to define waterboarding. They don't know if it's torture. If it is, it might be a little too tough, we can't be nice," Trump said during a campaign event in Gaffney, South Carolina.

Trump has previously referred to waterboarding as "sort of the least form of torture" or "the minimal form." And in the last week, Trump has called for the U.S. to go beyond waterboarding and use other methods of torture in its fight against radical Islamic terrorism.

The technique, which gives the detainee the sensation of being drowned, has been classified as torture by experts, international non-governmental organizations and top officials in both Democratic and Republican parties.

Read More