UNITED NATIONS (Reuters) - Russia’s foreign minister said on Friday the leaders of North Korea and the United States should tone down their bellicose rhetoric and warned that a collapse of a nuclear deal between Iran and world powers would only embolden Pyongyang. “The exchange of threats is quite bad, unacceptable,” Sergei Lavrov told reporters at a news conference.” We have to calm down the hot heads,” Lavrov said, adding that he was convinced a Russian-Chinese proposal could still pave the way for a diplomatic solution to the North Korea crisis. Lavrov added that a collapse of the Iran nuclear deal would give North Korea little incentive to drop its nuclear program in return for sanctions relief.  