According to one of the rebel commanders operating along the Syria-Jordan border, hundreds of US Marines and a large number of rebels have completed several days of live fire military exercises along the border.

These appear to be the continuation of live-fire exercises the Marines were carrying out last week at al-Tanf, which officials said were intended as a “warning to Russia,” after Russia warned they planned to act against Islamist factions in the area.

Pentagon officials today described the exercises as a “show of force,” saying that they want to demonstrate the ability of US forces to “respond to any threat to our forces within our area of operations.”

The US has warned a 55 km radius around al-Tanf is off limits to all other forces, though they’ve done little to prevent al-Qaeda forces from setting up shop in the area. It doesn’t appear the al-Qaeda forces were directly involved in the exercises, but they’ll clearly be the beneficiaries of the US preparing to “defend” the area from Syria and Russia.

There is no timetable for the operation in the south, but Russia informed the US it would be happening last week. This is likely to be a confrontation on the long-term US presence in Syria.

While US forces in Syrian Kurdistan are there at the behest of Kurdish officials, the Tanf base appears to serve little purpose, beyond giving the US a little presence in the southeast corner, where they can pick fights with any pro-government forces who get too close.