UNITED NATIONS - UN Secretary-General Ban Ki-moon condemned on Wednesday an attack at Aleppo University in Syria that killed scores of students and warned that the deliberate targeting of civilians was a war crime.

"Such heinous attacks are unacceptable and must stop immediately. All combating parties in Syria must abide by their obligations under international humanitarian law," Ban said in a statement. "Deliberate targeting of civilians and civilian targets constitutes a war crime."

Two explosions at Aleppo's university on Tuesday killed at least 87 people, many of them students attending exams. The cause of the explosions was not clear but the Syrian government and opposition activists blamed each other.

According to the United Nations, more than 60,000 people have been killed during a 22-month-old revolt against Syrian President Bashar Assad, which began with peaceful protests but turned violent after Assad's forces tried to crush the demonstrations.

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