I assume this was for force protection purposes to keep American forces there safe from attack.
It also sounds like these are likely Iran-affiliated forces rather than actual Syrian troops.
Is this an effort by pro-Assad forces to fill a vacuum left by ISIL pulling east?
UPDATE: I guess my impressions are mostly right:
U.S.-led coalition jets hit a convoy of Syrian and Iranian-backed militias that were heading towards the Tanf base in southern Syria where U.S. special forces are based, a rebel official with a Pentagon-backed rebel group said on Thursday
Muzahem al Saloum, from the Maghawir al Thwra group, told Reuters that the jets struck after rebel forces clashed with advancing Syrian and Iranian militias that were about 27 kms away from the base along the Damascus-Baghdad highway.
There were Syrian troops with the group advancing toward the border where we support rebels.
Although this makes it sound like the Syrians were part of an Iranian-organized militia--so not really a "Syrian" government force.
UPDATE: This incident may be related to this Iranian initiative:
Iran has changed the course of a land corridor that it aims to carve to the Mediterranean coast after officials in Iraq and Tehran feared a growing US military presence in north-eastern Syria had made its original path unviable.
The new corridor has been moved 140 miles south to avoid a buildup of US forces that has been assembled to fight Islamic State (Isis). It will now use the Isis-occupied town of Mayadin as a hub in eastern Syria, avoiding the Kurdish north-east, which had earlier been mooted by Iranian leaders as a crucial access route.
But the more southern route risks running through territory that has been abandoned by ISIL to fight America-backed rebels or that those rebels could take from ISIL.
So was this clash the result of an effort by Iran to take over territory abandoned by ISIL in order to secure an Iranian supply line to Syria and Lebanon?
UPDATE: No, apparently there were no Syrian troops. Just militias that appear to be Iranian sponsored:
US jets have attacked a convoy of Iranian-backed militiamen in south-eastern Syria in the first clash between the American military and forces loyal to Tehran since the US military returned to the region almost three years ago.
The airstrikes occurred near the Syrian town of al-Tanf, where Syrian opposition forces backed by the US have been under recent attack by Syrian and Russian jets near the main road linking Damascus to Baghdad. The militias, made up mainly of Iraqi Shia fighters, had been advancing towards the base throughout the week.
This is more of a strike on Iran than on Assad. The article notes the supply line linkage I mentioned.
Although this is the logical development of the war that President Obama began in Syria. At some point the parallel wars that Syria waged on non-jihadi rebels and the war we wage on ISIL and other jihadis as a de facto Assad ally would lead to a conflict between Assad's forces and the Syrians we back to fight ISIL.
So is our policy that Assad has to go, as Obama said? Or do we just want the Iranians to go?
UPDATE: I don't think the Russian protests are totally sincere. While Russia surely doesn't want our intervention to conclude with Assad hanging from a lamp post, the Russians don't want Iran to build up their influence in Iran.
UPDATE: The strike certainly bolsters our seriousness about this diplomatic effort:
U.S Secretary of State Rex Tillerson says a centerpiece of President Donald Trump's visit to Saudi Arabia is to curb any threats to the region posed by Iran.
Iran was definitely the focus of the strike.
