Russian air strikes in Syria have killed more civilians than they have Isil militants, despite Moscow's claims that its military intervention is intended to defeat the group.
Michael Fallon, Britain's Defence Secretary, said he "deplored" Moscow's use of unguided munitions on civilians and groups fighting the Syrian regime.
The Syrian Observatory for Human Rights said more than 1000 civilians had been killed during Russia's four-month bombing campaign. By comparison, the strikes had killed 893 Islamic State of Iraq and the Levant (Isil) fighters, and 1141 militants from other factions, the monitoring group said.
One of President Bashar al-Assad's staunchest allies, Russia began air strikes on the Government's behalf at the end of September.
Territorial gains have been limited but experts say Moscow has achieved its primary aim of shoring up the regime's northwest heartland in the face of rebel advances.
Under cover of Russian air power, Assad's forces have made progress around the second city of Aleppo and in southern Syria where Western-backed forces have held out for four years.
Last week, government troops also recaptured Salma, a town that held out for three years as a rare rebel stronghold in the coastal Latakia province.
Amnesty International said last month that Russia had "directly attacked" civilians in opposition-held areas before falsifying evidence to escape blame for possible war crimes.
But in interviews with The Daily Telegraph, civilians attested otherwise. In Idlib province, doctors spoke of multiple bombing raids on the area's last remaining health facility.
In the besieged Damascus suburb of Douma, teachers said their schools had been forced to close after Russian cluster bombs killed eight children at a local playground.
"They killed my son. And as I mourned for him, they killed my daughter too," said the parent of one of the children killed in that December 13 attack.
Moscow's more muscular role in the conflict has added to doubts about whether peace talks scheduled for next week will take place.