The victims, including 11 children and three women, were killed Monday when Syrian government forces dropped so-called barrel bombs -- barrels packed with explosives and shrapnel -- the Syrian Observatory for Human Rights said.
The organization, based in Britain, said the attack in Aleppo followed a weekend attack in which barrel bombs killed 126 people in the flashpoint city.
The organization said Assad's regime is responsible. The government has said its military operations are targeting "terrorist groups" in Aleppo neighborhoods.
"Each and every day that the barrel-bombing of Aleppo continues, the Assad regime reminds the world of its true colors," Kerry said in a statement. "It is the latest barbaric act of a regime that has committed organized, wholesale torture, used chemical weapons, and is starving whole communities by blocking delivery of food to Syrian civilians in urgent need."
Kerry said the use of barrel bombs is adding to an already "staggering civilian toll" in Syria's civil war.
"Each and every barrel bomb filled with metal shrapnel and fuel launched against innocent Syrians underscores the barbarity of a regime that has turned its country into a super magnet for terror," he said. "Given this horrific legacy, the Syrian people would never accept as legitimate a government including Assad."
CNN said it couldn't independently verify the authenticity of a video posted on the Internet of the weekend attacks in Aleppo or its death toll.
The Syrian Observatory for Human Rights said Monday Islamic militants fired five rockets at the village of Rabia'a in Hama province, killing at least five students. At least one rocket hit the village's high school.