"We have amassed evidence that weapons are being smuggled [to Syria] from outside, including through semi-legal organizations or even under protection of security agencies from other countries," he told the United Nations on Thursday.
The diplomat waned that Islamic militants were about to step up inroads into government-controlled territories, primarily near the northwestern city of Idlib. He added Daesh did not shy away from using children to stage terror attacks.
Nebenzia also said Russian armed forces had helped free over 1,400 towns and villages in Syria and bring over 96 percent of its territory back under government control, securing the return of over 1.5 million Syrian refugees.
Nebenzia noted that Al Qaeda* can fill the vacuum in Syria left by retreating Daesh fighters and become a major obstacle to the ongoing peace process.
"Our assessment is that Al Qaeda and its allies make take the initiative, becoming an obstacle to a peaceful settlement in Syria, as Daesh continues to crumble," he said.
*Daesh (also known as Islamic State, ISIS, ISIL or IS) and Al Qaeda are terror organizations, banned in US, Russia, and many other countries.