At least 30 people were killed and dozens more injured in Kabul on Saturday after a bomb went off outside a high school, The New York Times reports. The bombing happened just outside of Sayed Ul-Shuhada high school around 4 p.m., just as the school’s female students were ending their classes. Many of the wounded and killed were students, according to Dr. Mohammad Dawood Danish, a doctor at a hospital nearby. “The health condition of a number of girls is critical,” he was quoted saying.

Just before the blast, a witness said he saw a man behaving strangely in a Toyota parked outside the school. When he asked the man what was wrong, the man said, “None of your business.” The car exploded seconds later. Details about the attack remain unclear, including who was responsible. The Taliban has denied involvement. The bombing comes amid concerns that the U.S. troop withdrawal will lead to a surge in such violent attacks.