<p>WASHINGTON — More than 100 U.S. Marines were sent as reinforcements to a remote coalition outpost in southern Syria on Friday after Russia threatened to attack militants in the area, the Pentagon said.</p>
<p>The troops were flown by helicopter to the base at At Tanf — a small town near the borders of Syria, Iraq and Jordan. The base is used by U.S. special forces to train Syrian fighters who are confronting Islamic State militants.</p>