More than 18,000 people, nearly half of them civilians, have been killed in Russian air strikes on Syria since Moscow intervened exactly three years ago, a monitor said.
Russia, for its part, said its "accurate" strikes had killed 85,000 "terrorists".
A steadfast ally of Syria's ruling regime, Russia began carrying out bombing raids in the country on September 30, 2015 – more than four years into the 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 ISIS fighters were also killed in Russian strikes, with the rest of the dead including other rebels, the Britain-based monitor said.
Russia's defence commission published different figures on Sunday.
"All of the air strikes have targeted and are still accurately targeting terrorist targets," said commission chief Viktor Bondarev, cited by the Russian Interfax news agency.
Human rights groups and western governments have criticised Russia's air war in Syria, saying it bombs indiscriminately and targets civilian infrastructure — including hospitals.
The White Helmets, a Syrian rescue force that works in opposition areas, said in a report on Sunday that since 2015, it has responded to dozens of strikes by Russia on buildings used by civilians.
They included bombing raids on 19 schools, 12 public markets and 20 medical facilities, as well as 21 of its own rescue centres.
"Russia has flaunted its disregard for agreements over safe zones, no-conflict zones, cessations of hostilities, and de-escalation zones by continuing with air strikes on civilian spaces," the White Helmets stated.
Russia has operated a naval base in Syria's coastal Tartus province for decades, but expanded its operations to the nearby Hmeimim air base 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 areas of the country, including second city Aleppo in 2016 and areas around Damascus, the rural centre, and the south this year.
"The regime controlled just 26 per cent of Syrian territory [when Russia intervened]", said Mr Abdel Rahman. Now, it controlled almost two-thirds, he said.
In addition to the Russian and Syrian air forces, warplanes from the United States-led coalition fighting ISIS have carried 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 ISIS.
The Observatory, which relies on sources inside Syria for reports, says it determines whose planes carry out strikes according to type, location, flight patterns and munitions involved.