Russia's military said it has bombed 10 Islamic State of Iraq and the Levant (ISIL) group targets in Syria over the past 24 hours as it was expanding its aerial campaign.
Activists on Sunday, meanwhile, told Al Jazeera that there were civilian casualties in suspected Russian shelling on the central province of Homs.
Mahmoud Allouz, an activist in Homs, said two people were killed and 14 others injured in four air strikes on the villages of Ghernata, Umm Sharshouh, Talbeesa and Ghantou.
"Each air strike released six rockets," he said.
Russian defence ministry on Sunday said its jets "hit a terrorist training camp, including a suicide belt factory," without specifying the location of the strikes.
"Over the past 24 hours SU-34, SU-24M and SU-25 jets made 20 sorties," it said on its website.
"Ten infrastructure targets of ISIL bandit groups have been struck," it said, adding that the military were expanding their bombing campaign.
"As a result of our air strikes on ISIL targets, we have managed to disrupt their control system, the terrorist organisation's supply lines, and also caused significant damage to the infrastructure used to prepare acts of terror," the ministry said.
Since it launched an aerial campaign in Syria on Wednesday, Russia has been accused by Western officials and activists on the ground that Moscow's strikes were killing civilians, a claim that Moscow denies.
British Prime Minister David Cameron said on Sunday that Russia's decision to take military action in Syria to support Syrian President Bashar al-Assad was a "terrible mistake".
"They are backing the butcher Assad, which is a terrible mistake for them and for the world," Cameron told the BBC on the first day of his Conservative Party's annual conference in the northern English city of Manchester.
"It's going to make the region more unstable, it will lead to further radicalisation and increased terrorism. I would say to them 'change direction, join us in attacking ISIL'."
Cameron is keen for Britain to begin its own air strikes in Syria, joining allies in a US-led coalition against ISIL, a self-declared caliphate spanning large areas of Syria and neighbouring Iraq.
British bombing as part of the coalition so far has only targeted ISIL in Iraq.
He signalled that he would push ahead with plans for a vote in parliament to approve military action against ISIL in Syria, the Daily Telegraph newspaper said in its Sunday edition.