In a largely Shiite region of Afghanistan’s capital city, authorities said, explosions targeting educational institutions killed at least six people, including students, and injured 11 others.

According to Kabul police spokesman Khalid Zadran and the city’s Emergency Hospital, the explosives, which occurred in quick succession, were being investigated and more injuries were expected. A number of the injured were in serious condition.

The explosions took place inside the Abdul Rahim Shaheed High School and a few kilometers away in the Mumtaz Education Center, both in the Shiite Muslim district of Dasht-e-Barchi. At the Mumtaz Center, there were no early reports of casualties.

Guards on the two-story high school’s small street reported they observed ten casualties. An Associated Press video journalist spotted blood-splattered walls, charred notebooks, and children’s shoes inside the school.

The Associated Press spoke with numerous private security guards in the area, but they declined to reveal their names because they were afraid of retaliation from the Taliban security force that had cordoned off the region.

Witnesses claimed it looked a suicide bomber detonated a bomb inside the huge campus, which can house up to 1,000 pupils. The number of youngsters in the school at the time of the explosion was not immediately known.

After Afghanistan’s hardline Taliban rulers broke a pledge to allow all girls to attend school, the institution only teaches pupils until the sixth grade.

No one has claimed responsibility as of yet. The area has already been attacked by an Afghan affiliate of the deadly Islamic State terrorist group, which considers Shiite Muslims to be heretics.