The pictures were taken in 2015 at Russia's Hmeimim Air Base in Syria.
The US appears on the verge of striking the Syrian government after it allegedly carried out a gas attack in a suburb of Damascus over the weekend.
Russia has vowed to shoot down any US missile strike and repeatedly warned that any such strike on Syria could escalate hostilities.
"Russia vows to shoot down any and all missiles fired at Syria," President Donald Trump tweeted on Wednesday. "Get ready Russia, because they will be coming, nice and new and 'smart!'"
Russia's most advanced air defense system in Syria is the S-400, a very capable missile-defense system somewhat comparable to the US's MIM-104 Patriot, according to CSIS.
The photos below are of S-400 systems getting unloaded and set up at Russia's Hmeimim Air Base in Syria, showing what the US could face if Trump decides to strike.
Here's what it can do:
The S-400 Triumf, which NATO calls the SA-21 Growler, is a fourth-generation long-range missile-defense system that Russia began developing in 1993.
It's the successor to the S-200 and S-300 air-defense systems and became operational in 2007.
It's capable of taking out aircraft, drones, cruise missiles, and ballistic missiles in the terminal phase.
However, it does not have hit-to-kill ballistic-missile-defense technology, which means it can't physically collide with incoming warheads.
The S-400 has a range of about 150 miles to 249 miles.
On the low end of that range are the 48N6 missiles, which have 315-pound fragmentation warheads and can also hit ballistic missiles across a 37-mile radius.
On the high end of that range are the 40N6 missiles, but their deployment and true capabilities are unknown.
Russia is also testing the 77N6, designed specifically to take out ballistic missiles with hit-to-kill technology.
The S-400's radar can detect targets up to about 373 miles away.
Source: The National Interest
S-400s are currently deployed in Kaliningrad, Syria, and Crimea.
The CSIS map below shows where Russia's and NATO's air-defense systems are deployed.
You can see the full interactive map here.