Bloodstains are seen at a site hit by what activists said were three consecutive air strikes carried out by the Russian air force, the last which hit an ambulance, in the rebel-controlled area of Maaret al-Numan town in Idlib province, Syria January 12, 2016. REUTERS/Khalil Ashawi

AMMAN (Reuters) - Russian air strikes on Syria have killed nearly 1,400 civilians since Moscow started its aerial campaign nearly four months ago, a group monitoring the war said on Saturday.

The Britain-based Syrian Observatory for Human Rights, which collects information from a network of sources on the ground, said the Russian strikes had also killed 965 Islamic State fighters as well as 1,233 fighters from various other insurgent groups.

The main Syrian opposition group heading to Geneva peace talks on Saturday has demanded a halt to a joint Russian and Syrian bombing campaign they say targets mostly civilians in rebel held areas as a pre-condition for engaging in talks with the Syrian government.

Russia began a major aerial campaign on Sept. 30 to help its ally Syrian President Bashar al Assad. The air strikes tilted the war in Assad’s way after major setbacks earlier in 2015 brought rebel groups close to the coastal heartland of his Alawite sect.

Moscow says it is targeting Islamic State militants but rebels and residents say the Russian air strikes are causing hundreds of civilian casualties in indiscriminate bombing of civilian areas away from the frontline.