A reader asks: "Does the U.S. consider ISIS a threat to Saudi Arabia only if it kills Sunnis?"

"Islamic State is not a significant threat in Saudi Arabia, the U.S. military said on Friday, as it declined to speculate on the Sunni militant group's claim of responsibility for a deadly bombing at Shi'ite Muslim mosque. "In terms of Saudi Arabia and (Islamic State), we have no indication that they pose a significant threat at this time," said Colonel Patrick Ryder, a spokesman for the Pentagon's Central Command, which oversees U.S. forces in the Middle East."