The bombing Tuesday was the deadliest by President Bashar al-Assad's air force since Islamic State jihadists seized the city last year and declared it their capital.
It was not clear how many Islamic States members were killed, but the Syrian Observatory for Human Rights said more than half of the dead were civilians.
The US State Department yesterday condemned the strikes, and said the regime had no value for human life.
"The Assad regime's continued slaughter of Syrian civilians further exposes its callous disregard for human life."
She said Assad had lost his right to rule, and said his actions should be held accountable.
"We've been clear that Assad long ago lost all legitimacy to govern and that the Syrian regime must be held responsible for its brutality and atrocities against the Syrian people."
Psaki blamed Assad's government for continued human rights abuses and violating international law, accusing the regime of "murder, hostage-taking, enforced disappearances, torture, rape, sexual violence and the indiscriminate use of barrel bombs."
US President Barack Obama has rejected an alliance with Assad against the Islamic State group, arguing that any such pact would backfire.
Obama has said communication with the Assad regime was limited to informing them when they use Syrian air space in operations against the Islamic State jihadists.
