"The situation [in Syria] is very dangerous," Nebenzia said. "The immediate priority is to avert the danger of war."
The Russian envoy's remarks came as US President Donald Trump was weighing possible military strikes that could sharply escalate the conflict.
The envoy said Russia is very concerned about any escalation in Syria and expressed hope the United States would not allow the crisis in the country to deteriorate. Nebenzia also expressed Russia's desire to engage in dialogue about the recent events in Syria.
On Wednesday, US President Donald Trump threatened to take military action against Syria in response to an alleged chemical weapons attack in the Syrian town of Duma.
Reports of the alleged attack first emerged on Saturday, when rebel-allied groups said an apparent chemical attack killed up to 70 people.
The Syrian government has denied using chemical weapons in the Eastern Ghouta town of Duma, saying the alleged attack was staged by the terrorist group Jaish al-Islam to serve as a rallying call for intervention in Syria.
Russia's Foreign Ministry has said the goal of the reports of chemical attacks was to provide cover for terrorists and justify the use of military force against Assad. As early as March 13, Russian Air Forces were warning that terrorist groups in Eastern Ghouta were planning to stage a chemical attack as a provocation.