At least 19 students were injured on Tuesday in an explosion inside a university classroom in the Afghan city of Ghazni, an official said.

The explosion took place at around 9.40 a.m. inside the classroom of the Literature Faculty in the University of Ghazni while a session was underway, the provincial governor’s spokesperson, Arif Noori, told Efe news.

Noori said that 19 students, including 12 women, had been reported injured and two of them were in a critical condition.

The spokesperson added that preliminary investigation suggested explosives had been placed inside the classroom.

“Some of the students who are coming from remote and insecure areas of Ghazni province have contacts with the militants and we think they might be behind this blast,” Noori said.

The spokesperson said that many students had been detained earlier for allegedly having links with the militants.

No insurgent group has claimed the attack so far.

The attack comes a day after a bombing targeting a bus carrying army recruits in Nangarhar province killed 10 people and injured 27, most of them civilians.

Monday also marked the 18th anniversary of the beginning of the US’ war in Afghanistan, which started on October 7, 2001 with bombings on Taliban targets.