Russia has warned it will shoot down US missiles fired at Syria and target ships and planes that threatens the lives of its own troops.
Syria's most powerful ally has sparked fears of a major escalation in conflict should the US and its allies launch strikes on the Syrian regime over a suspected chemical attack on its own people.
Yesterday, it was reported Russia's ambassador to Lebanon, Alexander Zasypkin, said US missiles fired at Syria will be shot down and launch sites targeted.
In comments broadcast on Tuesday evening, said he was referring to a statement by Russian President Vladimir Putin and the Russian armed forces chief of staff.
US President Donald Trump tweeted: "Get ready Russia" as he reacted with fury to the remarks as he warned Moscow shouldn't be allies "with a Gas Killing Animal".
Here's what we know about Russian military capabilities in Syria.
'Triumph' S-400 surface-to-air missiles
An advanced truck-mounted system that Russia is known to have deployed to protect its Hmeymim air base in Syria's Latakia Province and its Tartus naval facility on the coast.
Its mobile nature means it can easily and quickly be deployed elsewhere.
Designed to shoot down military aircraft, missiles and drones, its radar can detect targets up to 600 Kms (375 miles) away.
Each truck carries four missiles of varying range and can track multiple targets simultaneously.
Taken seriously by NATO, the S-400s have not been combat tested however.
Capable of intercepting US Tomahawk cruise missiles, there are question marks over whether Moscow has enough interceptor missiles deployed to Syria to handle a large swarm of missiles.
In such a situation it might be able to shoot down some, but not all incoming missiles.
Russia also has an older version of the same missiles - S-300s - deployed in Syria.
Bastion coastal missile defence system
The Bastion system, thought to be deployed at or near Russia's Tartus naval facility, is an advanced mobile anti-ship and surface-to-surface defence system armed with two missiles.
Russian Defence Minister Sergei Shoigu has said the system can hit sea targets at a distance of 350 km (219 miles) and land targets at a distance of 450 km (281 miles).
Russia used the system to launch a coordinate strike against rebels in Syria in 2016.
The Syrian army is also thought to have bought the Bastion system from Russia.
Pantsir-S1
A truck-mounted short to medium range surface-to-air missile and anti-aircraft artillery weapons system possessed by both Russian and Syrian government forces in Syria.
Known to be deployed by Russia at or near its Hmeymim air base and at its Tartus naval facility.
Has been fired in Syria a number of times to take out drones and missiles. Can shoot down cruise missiles.
Warships
Russia has between 10 and 15 warships and support vessels deployed in the Mediterranean.
They include the Admiral Grigorovich and Admiral Essen frigates, which are armed with cruise missiles, as well as submarines.
According to a senior Russian politician and satellite imagery, most of the ships have left Russia's Tartus naval facility "for their own safety."
Russian daily Kommersant said they were taking part in a long live fire war game close to the Syrian coast intended as a show of force. It said Russia had also deployed Il-38N submarine hunter aircraft.
Military aircraft
Russia is estimated to have dozens of war planes and helicopters at its Hmeymim air base in Syria's Latakia Province including fighters, bombers and multi-role aircraft.
It is also reported to use another Syrian base for its helicopter gunships.
Moscow is able to mobilise powerful long-range strategic bombers from Russia itself to carry out bombing runs and has also fired cruise missiles in the past from ships in the Caspian Sea.