The streets of Aleppo were strewn with destroyed buildings and dead bodies Monday after several areas of the besieged Syrian city were captured by government forces, a humanitarian group reported on social media late Monday.
The White Helmets, a group of volunteer search and rescue workers that operates in rebel-held Syria, documented a particularly deadly day in eastern Aleppo, where Syria's military says pro-government forces now control 98 percent of the region.
On Twitter, the White Helmets described the scene as "hell."
Seven-year-old Bana al-Abed, whose Twitter account has become a haunting window into life inside opposition-held Aleppo, also tweeted about the desolation Monday. Al-Abed and her mother, Fatemah, tweeted last month that they were "on the run" as Syrian President Bashar al-Assad's attacks on Aleppo intensified.
Government forces already control the west of Aleppo and recapturing the city — Syria's biggest, before the civil war — would be the greatest prize so far for Assad in the six years of conflict.
Swaths of the country remain in rebel hands, however, and ISIS on Sunday seized the historic city of Palmyra.
In a statement Monday, Russia's military wing in Syria said pro-government forces were in "full control" of most of Aleppo, adding that the "territory still controlled by the militants in eastern part of the city is no more than [4 square miles]."
The United Nations, meanwhile, said it was "alarmed" by reports of civilian casualties.
"While stressing that the United Nations is not able to independently verify these reports, the Secretary-General is conveying his grave concern to the relevant parties," said the spokesperson for the Secretary-General, in a statement. "He has instructed his Special Envoy for Syria to follow up urgently with the parties concerned."
The statement added: "The United Nations underlines the obligation of all parties on the ground to protect civilians and abide by international humanitarian and human rights law. This is particularly the responsibility of the Syrian Government and its allies."