Opposition videos published online by The New York Times appear to show the Syrian air force firing missiles at Aleppo University in northwest Syria. At least 82 people were killed and another 162 wounded Tuesday as students there started their first day of exams.
U.N. Secretary-General Ban Ki-moon, in a statement issued through his spokesman's office, called for an investigation into possible war crimes associated with the attack.
"Deliberate targeting of civilians and civilian targets constitutes a war crime," his statement read. "Such heinous attacks are unacceptable and must stop immediately."
Victoria Nuland, a spokeswoman for the U.S. State Department, said Washington was appalled by the attack. Most of the victims, she said, were students. Any attack on unarmed civilians is a violation of international law that must be investigated, she added.
In August, Human Rights Watch reported that Syrian fighter jets dropped bombs on a residential neighborhood in Aleppo province, flattening homes and leaving 40 people dead.
A 2012 report from a U.N. commission on the Syrian crisis found evidence that both parties to the conflict in Syria committed war crimes, though those carried out by pro-government forces were more severe.
The United Nations estimates that more than 60,000 people have died as a result of conflict in Syria that began in early 2011.