Russia, a steadfast ally of Syria's ruling regime, began carrying out bombing raids in the country on September 30, 2015 -- more than four years into the devastating conflict.

Since then, they have killed 18,096 people, according to the Syrian Observatory for Human Rights.

"That number includes 7,988 civilians, or nearly half of the total," said Observatory chief Rami Abdel Rahman.

Another 5,233 Islamic State fighters were also killed in Russian strikes, with the rest of the dead including other rebels, Islamists, and jihadists, the Britain-based monitor said.

Russia has operated a naval base in Syria's coastal Tartus province for decades, but expanded its operations to the nearby Hmeimim airbase in 2015.

It also has special forces and military police units on the ground in government-controlled parts of the country.

The air strikes were crucial in helping troops loyal to President Bashar al-Assad retake swathes of the country, including second city Aleppo in 2016 and areas around Damascus, the rural centre, and the south this year alone.

"The regime controlled just 26 percent of Syrian territory" when Russia intervened, said Abdel Rahman, compared with close to two-thirds now.

But human rights groups and Western governments have criticised Russia's air war in Syria, saying it bombs indiscriminately and targets civilian infrastructure including hospitals.

In addition to the Russian and Syrian air forces, warplanes from the US-led coalition fighting IS have also been carrying out bombing raids on Syria since September 2014.

Last week, the Observatory said that US-led coalition air strikes on Syria had killed more than 3,300 civilians since the alliance began operations against IS targets there in 2014.

The Observatory, which relies on sources inside Syria for its reports, says it determines whose planes carried out strikes according to type, location, flight patterns and munitions involved.