Syrian government forces have recaptured all of the areas taken by rebel fighters in a recent assault intended to break the regime siege on eastern Aleppo, a monitor said Saturday.
The Syrian Observatory for Human Rights said the army had recaptured key areas including the western district of Dahiyet al-Assad and the village of Minyan outside the city.
Regime forces also advanced south of the city, seizing two areas from the rebels.
The reversals undo all of the progress made during a recent push by opposition fighters, including former Al-Qaeda affiliate Fateh al-Sham front, as they tried to end a government siege on the east of Aleppo city.
Government forces surrounded the city's rebel-held east in July, severing the last supply line into opposition neighbourhoods and imposing a blockade that has led to food and fuel shortages.
Rebels have tried several times to break the siege, succeeding briefly in August, but no aid has entered east Aleppo since July.
The monitor said that more than 450 fighters and civilians had been killed since the rebels began their latest bid to break the siege on October 28.
The dead include 215 Syrian and foreign opposition fighters, including some who carried out suicide bomb attacks, and 143 regime forces.
Nearly 100 civilians have also been killed, the majority of them in government-held west Aleppo where 30 children were among those killed in waves of rebel rocket fire.
Five civilians including one child were killed on Saturday in rebel shelling of government-held sectors of the city, the Observatory said.
And a reporter working for Iran's state television channel IRIB was killed on Saturday in a rebel mortar attack in Minyan, the broadcaster said.
Iran supports President Bashar al-Assad's regime.
Once Syria's economic powerhouse, Aleppo has been ravaged by the war that began with anti-government protests in March 2011.
The city has been divided since mid-2012, and in September, the government announced an operation to recapture all of Aleppo.
The government assault, backed by Russian warplanes, has killed hundreds of people in east Aleppo and damaged and destroyed infrastructure including hospitals.
A flotilla of Russian warships including the aircraft carrier Admiral Kuznetsov is now in the eastern Mediterranean off Syria's coast, a naval commander has confirmed.
Russia's Interfax news agency had on Friday cited a Russian military and diplomatic source as saying that MiG and Sukhoi jets have been regularly flying into Syrian airspace from the Kuznetsov to "determine combat missions".
More than 300,000 people have been killed in Syria's five-year war.