Russian foreign minister Sergey Lavrov has warned Syrian rebels in Aleppo that they will be wiped out unless they agree to stop fighting and quit the besieged city.
Mr Lavrov said that "those who refuse to leave nicely will be destroyed", adding: "There is no other way."
Mr Lavrov also lamented what he described as attempts by the United States to obtain a pause in the fighting in Aleppo to allow rebels to re-arm and re-supply.
He said that "serious conversations with our American partners are not working".
Syrian government forces are closely backed by Russian air power in the Middle East country's civil war.
Government forces recently launched a new push to retake rebel-held eastern Aleppo neighbourhoods and seized large parts of the city.
Meanwhile, a spokesman for Russian President Vladimir Putin said the Kremlin regrets a "more than modest" reaction by the international community following the deadly attack on a Russian military hospital in Aleppo on Monday.
Dmitry Peskov singled out the United States for what he said was a muted reaction to the "tragedy" in the Syrian city. Two Russian nurses were killed in the attack.
Russian officials have said the artillery attack was deliberately planned and suggested that the coordinates of the hospital were supplied to rebels in Aleppo by a foreign power.
Russia's defence ministry said a statement from the International Red Cross about the incident was "cynical" and showed the organisation was "indifferent to the murder of Russian medics in Aleppo".
The Syrian government said it rejects any ceasefire for Aleppo unless it includes the departure of all rebels from the eastern part of the city.
Syria's foreign ministry said in a statement carried on the state SANA news agency that the government will not allow the rebels a chance to "regroup and repeat their crimes" in the divided city.
The statement comes a day after Russia and China blocked a draft resolution at the UN Security Council demanding a seven-day truce in Aleppo.
The Britain-based Syrian Observatory for Human Rights said rebel shelling of Aleppo's government-held districts killed 81 civilians in the past three weeks. The government's offensive to take eastern Aleppo killed 341 civilians over the same period and displaced tens of thousands over the past week.