Syrian President Bashar Assad's government has been buying oil from the Islamic State group, which has made over $500 million so far through the trade, a top U.S. Treasury official said Thursday. Adam Szubin added that some of the ISIS oil went to Turkey -- an allegation also made by Moscow after Ankara downed a Russian fighter jet on the Syrian border late November. Szubin, speaking at Chatham House in London, said that the militant group, also known as ISIS or ISIL, was selling $40 million a month worth of oil, which is sent on trucks across the battlefront of...