WASHINGTON (CNN) — U.S. military commanders in the Middle East have been sent a highly classified message reminding American forces to maintain discipline and prudence if they encounter any Iranian military or security forces during potential unrest surrounding Iran’s presidential election, CNN has learned. This so far is the only acknowledged U.S. military reaction to the unfolding situation in Iran. Two U.S. defense officials with direct knowledge of the message confirmed the details to CNN but said the issue is so sensitive that they could not divulge whose signature was on the message. It was distributed via secure communications in...