WASHINGTON (Reuters) - U.S. Defense Secretary Jim Mattis said on Monday that Russia s bombing of U.S-backed fighters in Syria was being discussed at the highest levels and while a communication link between the two countries had worked to avoid such incidents, the strike over the weekend was a departure.  When you look at the fact that this is a change, you can imagine this is at the highest levels,  Mattis told reporters. Russia s Defense Ministry on Sunday rejected the allegations, saying its planes only targeted Islamic State militants and that it had warned the United States well in advance of its operational plans. 
Russian bombing of U.S.-backed forces being discussed at 'highest levels': Mattis