Vance appeared to indicate that the United States was still interested in diplomacy, after Trump threatened force if Iran's clerical state does not agree on key concerns starting with its nuclear program.

"In some ways, it went well; they agreed to meet afterwards," Vance said in a Fox News interview.

"But in other ways, it was very clear that the president has set some red lines that the Iranians are not yet willing to actually acknowledge and work through," Vance told "The Story with Martha MacCallum" program.

"We're going to keep on working it. But of course, the president reserves the ability to say when he thinks that diplomacy has reached its natural end," Vance said.

"We hope we don't get to that point, but if we do that will be the president's call."