The Syrian National Council opposition group says Russian air strikes north of Homs city killed 36 civilians, including five children and one member of the civil defense units known as the White Helmets.
Khaled Khoja, leader of the SNC, considered the main Western-backed Syrian opposition group, said at a press conference at the United Nations Wednesday that the strikes also hit a base of the Free Syrian Army but resulted in no casualties. He said there are no Islamic State group forces in the four areas struck Wednesday.
The claim could not be independently verified.
"Russian claims that they are there to fight IS are baseless. That was proven today," he said.
Russia is "using its military force to support the Assad regime's war against civilians. And it risks implicating itself in war crimes," he warned, urging the international community to call for "the enforcement of a ban on aerial bombardment" in Syria.
He called Russia an occupying force and called for a "war of liberation" against Russian forces.
Russia's Foreign Ministry dismissed the claims of civilian deaths from Khoja and others, saying they are false and part of an "information war."
A spokeswoman for the ministry on Wednesday said Khoja's accusations "were published even before the airstrikes started."
The spokeswoman told reporters on the sidelines of the UN General Assembly in New York that Russia is acting "absolutely, legitimately" according to international law.
"Honestly, I don't understand what is the difference between the French air bombings and Russia's. There's only one difference, we're acting according to a request from Damascus," she added.
Also Wednesday, the UN secretary general said airstrikes by any country in Syria must strictly observe international humanitarian and human rights law.
A spokesman for Ban Ki-moon told reporters Wednesday that all efforts must be made to spare civilians, and reports of civilian deaths must be swiftly investigated.
Stephane Dujarric added that "without genuine commitment by the international community to support a parallel political process that meets the legitimate aspirations of the Syrian people, it will not be possible to end the Syrian conflict and ultimately to defeat" the Islamic State group.