Russian Federation and the United States failed on Tuesday to win support at the UN Security Council for their rival proposals to investigate chemical weapons use in Syria as the threat of military action loomed large.
Resolutions drafted by each country have been rejected at the UN Security Council.
Moscow opposes any Western strike on its close ally Assad and has vetoed Security Council action on Syria 12 times since the conflict started.
After the second Russian measure was defeated, Nebenzia addressed US Ambassador Nikki Haley directly, appealing to the United States to refrain from military action.
USA president Donald Trump and Western allies are discussing possible military action to punish Assad for a suspected poison gas attack on Saturday on a rebel-held town that long had held out against government forces.
Russian Federation and the United States clashed at the United Nations Security Council on Tuesday after Moscow vetoed a Washington-drafted resolution to set up a panel to identify the perpetrators of toxic gas attacks after chemical weapons were used in the rebel-held town of Douma in Syria's Eastern Ghouta.
Six Council members - Bolivia, China, Ethiopia, Equatorial Guinea, Kazakhstan and Russian Federation voted in favour of the draft while seven against (France, the Netherlands, Peru, Poland, Sweden, United Kingdom and United States) and two abstentions (Cote d'Ivoire and Kuwait).
The US draft for creating a mechanism along with the authority to assign blame for chemical attacks in Syria, the was vetoed by Russian Federation at first.
"History will record that, on this day, Russian Federation chose protecting a monster over the lives of the Syrian people", Haley was quoted, as saying, while referring to Syrian President Assad.More news: PSG star Neymar reveals which game he expects to return for
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Worldwide chemical weapons experts are expected to go to Douma to investigate the suspected poison gas attack.
Mr Nebenzia said the resolution was an attempt to recreate the old expert body, whose extension Moscow blocked in November.
Vladimir Shamanov, a retired general who heads the defense affairs committee in the lower house of parliament, said in televised remarks Tuesday that a US strike in Syria could hurt Russian servicemen and trigger Russian retaliation.
US President Donald Trump has cancelled a trip to the Summit of the Americas in Peru's Lima, citing the Syrian developments and on Tuesday conferred with National Security Adviser John Bolton and defence officials.
Damascus also mobilized overnight Tuesday, according to the Syrian Observatory for Human Rights, which said the army had "put all military positions on alert, including airports and all bases, for a period of 72 hours". A US Navy guided-missile destroyer, the USS Donald Cook, is in the Mediterranean.
In the meantime, the worldwide chemical weapons watchdog, the Organization for the Prohibition of Chemical Weapons, said it will send a fact-finding mission to Douma to investigate the reported attack.
The White House said that, in a telephone call, Trump and British Prime Minister Theresa May "agreed not to allow the use of chemical weapons to continue".
Both leaders agreed the global community needs to respond to uphold the worldwide prohibition on the use of chemical weapons.