Stephen Harper is calling on Russia to stop blocking United Nations attempts to impose sanctions on the "murderous" Syrian regime of Bashar Assad.

The prime minister singled out Russia by name during question period Wednesday, urging it to join in the international effort to impose binding sanctions on the Assad regime.

Russia is a permanent member of the UN Security Council, and has opposed any use of force to remove Assad, or any resolutions on sanctions.

Canada has been attempting to persuade Russia to stop supporting its long-time Middle East ally as part of a broader effort led by the United States.

'We have all witnessed the horrors in Syria with the Assad regime, where innocent children are now being targeted. Canadians feel the pain of the Syrian people.'—Tom Mulcair, federal NDP leader

"We encourage Russia and others to join with us to apply binding sanctions against what is a murderous regime," Harper said, calling the Syrian situation unacceptable to Canadians and the international community.

Harper also appeared to be referring to China, the other permanent member of the security council that has backed Syria.

Harper spoke in response to a question by NDP Leader Tom Mulcair, who asked the prime minister specifically about diplomatic attempts to sway Russia.

"We have all witnessed the horrors in Syria with the Assad regime, where innocent children are now being targeted," Mulcair said.

"Canadians feel the pain of the Syrian people."

A UN report released earlier this week accused Syria government forces and their militias of abusing children as young as nine. It accused them of killing and maiming, arbitrary arrest, detention, torture, and sexual violence, and using children as human shields.

U.S. Secretary of State Hillary Clinton warned this week that the Syrian conflict could escalate dramatically because Russia is sending attack helicopters to Syria for use by the Assad regime.

Russian Foreign Minister Sergey Lavrov has denied the claim.