The Syrian army carried out air raids on the city Aleppo, leaving about 90 people dead, including women and children, officials said.
The raids, which targeted opposition strongholds, took place Saturday, CNN reported Sunday.
"The humanitarian situation is very bad, there is a huge number of wounded people," an unnamed medical staffer from a field hospital in Aleppo told CNN. "I am so nervous because my staff inside (have) become so confused, I have to calm them, I don't know what I will have to do for tomorrow.
"The situation is very urgent," the medic said. "We need U.S. pressure on the regime for us to be able to take a breath, to have them stop this aggressive shelling on Aleppo."
A renewed round of peace talks between President Bashar Assad's regime and the opposition concluded in Geneva Friday with no progress reported.
"This is a modest beginning, but it is a beginning on which we can build," U.N.-Arab League Joint Special Representative Lakhdar Brahimi told reporters after the talks ended Friday.
The United Nations put the death toll in the Syrian civil war, which started in 2011, at more than 100,000.