Syrian rebels cut the main supply route to the part of the city held by the regime, and Assad's army is fighting back hard.
The messages came as the Syrian government has cut off rebel-held Aleppo from the outside world, potentially trapping the 250,000 people who live there in a violent siege without food, medicine, and other staples.
The Syrian army used artillery to advance closer to Aleppo's strategically important Castello Road, bringing government forces closer to their long-standing objective of encircling rebel-held areas of Aleppo.
The powerful Islamist Nusra Front is ideologically opposed to the more moderate Syrian rebels and their Western supporters, but occasionally fights alongside them against the Islamic State.
FBI Director James Comey said there's no evidence that the shooter was part of a larger conspiracy or directed by an extremist group like the Islamic State.
The London-based Syrian Observatory for Human Rights said Russian warplanes targeted civilian areas around the city's national hospital and other neighborhoods held by a coalition of hardline Islamist rebel groups.
The Syrian Observatory for Human Rights says it arrived at the number by adding up death tolls provided by sources in several Syrian jails and security agencies.
Hezbollah said Saturday that the death of its top commander in Syria was the result of rebel shelling, and not an Israeli airstrike.
Dozens of air strikes hit near the town of Khan Touman, which rebels took from forces loyal to the government and its ally Iran late on Thursday.
After nearly two weeks of brutal shelling and urban combat, Russia and the United States have declared a tentative ceasefire in Syria's second-largest city.
It appears that Syrian government forces plan to mount an offensive to retake Aleppo, where more than 100 people have reportedly been killed over the past week.
Diplomats and Syrian factions say the ceasefire will not collapse as long as the US and Russia support it, but the fighting is actually intensifying in some places.