A UN Security Council resolution that would have demanded a seven-day truce in Syria's Aleppo, which New Zealand helped draft, has been vetoed with the country's UN representative saying he was "bitterly disappointed".
Moscow, a close ally of Assad's government, launched a military intervention in support of Damascus past year.
Russian Federation plans to conduct talks with the United States later this week about imposing a deadline for rebels to leave the area, Foreign Minister Sergei Lavrov said Monday.
This is the second loss of an aircraft from the Admiral Kuznetsov since it arrived off Syria last month.
He told a news conference once the deal was reached, rebels who stay in the besieged eastern part of the city will be treated as terrorists and Russian Federation will support the operation of the Syrian army against them.
Despite calm witnessed at the Idlib fronts controlled by opposition factions, the city has been subject to a military campaign launched by the regime and Russian Federation two weeks ago.
The resolution comes as regime forces continue incursions into the eastern neighborhoods of Aleppo, and sieze control of the main road to the Aleppo airport.
About 15,000 rebel fighters were in the city before the assault began, according to the Britain-based Syrian Observatory for Human Rights.
US deputy ambassador to the UN, Michele Sison, blamed Moscow for the worldwide community's failure to bring about an end to violence in Syria "because Russian Federation is more concerned with preserving its military gains".
"The revolutionaries will not leave Aleppo and will fight the Russian and Iranian occupation until the last drop of blood", said Abu Abdel Rahman al-Hamawi of the Army of Islam, another smaller rebel group active in Aleppo.
The UN estimates more than 31,000 people have fled their homes to areas held by the government or Kurdish forces, or deeper into the embattled city. He said the army has already retaken more than half of the neighbourhoods in eastern Aleppo, and that special forces would lead the battle in the narrow streets of the city's historic district.
The United States has backed the rebel groups and has called on Assad to step down and cede power in Syria.
The Syrian army has vowed to crush the rebels in Aleppo.
Lavrov stated that by the United States request the consultations over Eastern Aleppo in Geneva were postponed until December 6-7.
But it has sent field hospitals to the city. "They're now in control of about 60 percent of what used to be the rebel-controlled east", Al Jazeera's Stefanie Dekker said, reporting from Gaziantep along the Turkey-Syria border.
Activists said the Syrian forces advanced in the al-Sha'ar neighborhood in eastern Aleppo and have become so close to the rebel-held areas in the ancient part of the city.