Human Rights Watch, in a report published last weekend, said it reviewed video evidence that suggested Syrian forces are using RBK-20 and AO-1SCh cluster bombs during conflict with rebel forces.
"Cluster bombs have been comprehensively banned by most nations, and Syria should immediately stop all use of these indiscriminate weapons that continue to kill and maim for years," said Steve Goose, arms director at Human Rights Watch, in a statement.
Russian Foreign Minister Sergei Lavrov said there was nothing in the evidence to suggest his government was behind the munitions.
"There are loads of weapons in this region, including in Syria and other countries of the region, and arms are supplied there in large quantities and illegally," he was quoted by Russia's state-run news agency RIA Novosti as saying. "It is very difficult to establish from where and how ammunition and weapons are supplied there."
China, Russia, the United States and Syria are among the countries that haven't signed a comprehensive ban on cluster bombs. Russia's military ties to Syria have been criticized over the course of the civil war there.
Human Rights Watch said it believed the cluster bombs were from the Soviet-era, noting "there is no information available on how or when Syria acquired them."