Nicholas Blanford at CSM (via Jonathan Spyer):

US-backed forces announced Tuesday that they had begun the long-awaited assault on the northeastern Syrian city of Raqqa, the so-called Islamic State's main stronghold in the country and its self-declared capital.

But some 170 miles to the south, in a remote corner of Syria’s southeastern desert, another clash is brewing that is pitting the strategic objectives of the United States against those of Iran, and that could soon bring US troops and Iranian-backed forces into direct military confrontation.

Both US and Russian warplanes have been deployed, and some shots have already been fired, including by US-backed coalition forces on Tuesday, the US military said.

The clash is over a military garrison at Tanf, located near a border crossing on a highway that cuts through hundreds of miles of flat desert. It was captured from jihadist forces more than a year ago and is being used by US Special Forces and allies to train Syrian militias to fight ISIS, which controls territory to the northeast. ...