White House press secretary Karoline Leavitt said US forces were "very close to meeting the core objectives" of the military action against Iran.

She told reporters that "productive conversations" with Iran were ongoing but stressed more strikes could come if they're unsuccessful.

"If Iran fails to accept the reality of the current moment, if they fail to understand that they have been defeated militarily ... Trump will ensure they are hit harder than they have ever been hit before," Leavitt said at a briefing on Wednesday.

"President Trump does not bluff and he is prepared to unleash hell," she said. "Iran should not miscalculate again."