The Syria hotline for US and Russian militaries

Russia has said it is suspending a special hotline to communicate with the US-led coalition about operations in Syria, raising the risk of a military mishap.

Here is a quick look at the so-called "deconfliction line" and why it has become so important in Syria.

- What is it? -

The line was established in October 2015 after Russia entered Syria's civil war to prop up President Bashar al-Assad.

Both sides agreed to open a regular communications channel after several instances in which Russian and US planes or drones had come close to each other, raising the nightmare prospect of a mid-air collision or some other dangerous encounter.

The link is just a regular phone line staffed on the US side by a Russian-speaking officer in an operations center at a base in Qatar, and has been used almost daily since its inception.

- What has happened? -

On Sunday, a US jet shot down a regime warplane in northern Syria as it "dropped bombs" on US-backed local forces.

Russia condemned the action and said it would sever the deconfliction line.

Moscow made a similar threat in April after the United States launched a cruise missile attack on a regime air base in retaliation for a suspected chemical weapons strike on civilians.

- The implications -

It later emerged that Russia and the United States continued to use the hotline even after Moscow said it was hanging up.

It is possible a similar pattern is emerging in this instance.

As on the previous occasion, the Pentagon will not answer whether it is still using the hotline, deferring questions to the Russians.

"We believe that having a channel where we can de-escalate and understand each other's intentions serves a very good purpose and we are hopeful that we can continue to use it," Pentagon spokesman Navy Captain Jeff Davis said Tuesday.

- Does it work? -

Generally, yes. But the system is not perfect, especially when it comes to trying to pass messages to the Syrian regime.

Sunday's downing of a regime plane and an incident this month when an American jet shot down a pro-regime drone illustrate the line's limitations.

The Russians "don't have operational control over the Syrian forces or the pro-regime militias," Davis noted.