Syrian activists and state media say government forces and their allies have seized control of all areas of Aleppo’s Old City that had been held by rebels, who are calling for a five-day humanitarian truce in the city.
Six Western powers called for a cease-fire to allow for aid to be brought into remaining rebel-held areas of Aleppo, warning that "a humanitarian disaster" is unfolding.
The British-based Syrian Observatory for Human Rights said on December 7 that rebel fighters withdrew from the last parts of the Old City under their control after the army seized the districts of Bab al-Hadid and Aqyul.
State media also said the military had taken over the Old City, while Reconciliation Minister Ali Haidar called the army's advance a "strategic victory."
The monitoring group said the military and allied forces now hold about 75 percent of eastern Aleppo, which the rebels had been holding for the past four years, three weeks into their operation to capture all of the city.
The capture of Aleppo, the rebels' last urban stronghold, would represent the biggest military victory for Syrian President Bashar al-Assad since the civil war erupted following a government crackdown on pro-democracy protests in 2011.
Meanwhile, rebels in Aleppo called for an immediate five-day cease-fire and for the evacuation of civilians and around 500 critical medical cases.
The plan signed in the name of the Aleppo Leadership Council also asked for all involved parties to discuss the future of the city once the humanitarian situation in the rebel-held sector has been alleviated.
The United States, Britain, and France later led a call from six countries for an "immediate cease-fire."
In a statement also backed by Canada, Germany, and Italy, they denounced Assad's government and Russia for "their obstruction of humanitarian aid."
The government's "refusal to engage in a serious political process also highlights the unwillingness of both Russia and Iran to work for a political solution," they also said.
Assad's government and its ally Russia have rejected a cease-fire for Aleppo, Syria's second-largest city, where tens of thousands of civilians are trapped.
At least 80,000 people have fled eastern Aleppo since the military offensive backed by heavy air strikes and artillery fire began in mid-November, according to the observatory.
The figure includes residents who have sought refuge in the government-held western section of the city and a Kurdish-controlled area. However, it does not include others who have fled south to remaining rebel-held territory.
The observatory said at least 15 people, including a child, were killed in government fire on east Aleppo on December 6, and three children were among 11 people killed by rebel fire on government-held areas of the city.
Russian Colonel Killed
In another development, Syrian state news agency SANA reported that several Israeli missiles targeted a military air base outside the capital, Damascus, overnight, causing a fire but no casualties.
Also on December 7, Russia’s Defense Ministry said a Russian military adviser, identified as Colonel Ruslan Galitsky, had died after being wounded in what it said was rebel shelling of a government-controlled neighborhood several days earlier.
The statement did not specify where or when exactly Galitsky died but said he had already been awarded a posthumous military award.
The colonel was one of the highest ranking Russian servicemen among the roughly 20 Moscow says have been killed in Syria.
The fatality marks Russia's third in Syria this week. The Defense Ministry said on December 5 that two female medics were killed by what it said was the rebel shelling of a makeshift Russian military hospital in Aleppo.
Russia has been flying air raids in Syria since September 2015 and has provided longtime ally Assad's forces with other military support during the war, which has killed at least 250,000 people and driven many more from their homes.
The Kremlin said on December 7 that a potential U.S.-Russia deal to allow Syrian rebels to safely leave Aleppo was still on the agenda.
On December 6, Russian Foreign Minister Sergei Lavrov accused the United States of canceling a meeting this week to discuss the fate of rebel forces in Aleppo, and declared that fighters who refuse to leave the city would be "eradicated."
U.S. State Department spokesman Mark Toner rejected the accusation, saying the United States had never confirmed that talks would take place this week.
Meanwhile, U.S. Secretary of State John Kerry conceded that rebels might lose control of Aleppo, but said negotiations would still be needed to end the war.
Kerry said he hopes Russia will "understand the imperative of getting to that table, having the negotiation and of not inflaming passions more with the total destruction of Aleppo."
And French President Francois Hollande sharply criticized Moscow after Russia and China earlier this week vetoed a proposed UN Security Council resolution calling for a seven-day cease-fire in Aleppo.
"Russia's systematic obstruction bolsters the regime of Bashar al-Assad in its destructive drive which is harming the defenceless civilian population," a statement from Hollande's office said.
The Russian Foreign Ministry announced that Lavrov would hold talks with Kerry and German Foreign Minister Frank-Walter Steinmeier in Hamburg later on December 7.
The three are due to take part in a meeting of the Organization for Security and Cooperation in Europe in the German city on December 8-9.
With reporting by Reuters, AFP, dpa, TASS, and RT