title: Russian bombing of U.S.-backed forces being discussed at 'highest levels': Mattis
text: 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. 