From Fox News:
The Russian Su-27 jet had air-to-air missiles under its wings and approached the U.S. Air Force RC-135 recon jet “rapidly,” coming within five feet of the American aircraft, the officials said.
Once alongside, the Russian jet was “provocative” in its flight maneuvers and flying “erratically,” according to another official.
From the Independent:
Russia has said it will treat US warplanes operating in parts of Syria where its air forces are present as “targets” amid a diplomatic row caused by the downing of a Syrian jet.