Icahn, the billionaire investor, called Trump, the real estate mogul turned U.S. presidential candidate, to ask for an explanation after Trump made the comments in a speech.

After that conversation, Trump told Reuters in a phone interview that he did not mean to include Icahn in his characterization.

Trump, who is leading the Republican field in the polls by a wide margin, was telling the audience at a rally in Greenville, South Carolina, that the U.S. needed strong negotiators in key government roles. He said he preferred effective dealmakers like Icahn to "nice" people who, he said, were powerless in their roles.

"Carl Icahn's one of the best," Trump said in the speech. "If I put Carl in charge of Japan, 'Carl: Handle Japan trade deals.' It's over, just walk away."

Trump quickly added: "The people I'm talking about are not nice people. They're vicious horrible miserable human beings. But they're the greatest negotiators in the world ... These are terrible people in many cases. In about 2 percent of the cases they're actually nice people."

Icahn declined to comment for this story. A spokeswoman for Trump confirmed Icahn made the call.

Icahn made his fortune and developed a reputation on Wall Street as a "corporate raider" in the 1980s. He is now heralded as one of the best shareholder activists in the world for pushing some of the biggest companies including Apple Inc to use some of their excess cash for dividends and buybacks.

In the Reuters interview, Trump stressed that he saw Icahn as part of the "nice" 2 percent of strong business negotiators.

Trump has been saying for months he would include Icahn, 79, in his cabinet if he were elected president. At first, the proposal was to make him Treasury Secretary but Icahn rejected that as a possibility in June.

Now, Trump is talking about making him some kind of powerful trade negotiator, Icahn has yet to publicly respond to that suggestion.