Israel’s military on Monday targeted Iran’s Evin prison, a notorious detention facility in Tehran where dissidents and political prisoners are held. The detention center has long been regarded as a symbol of repression, and human rights groups and survivors say that torture and executions are routine there.

Israel’s defense minister, Israel Katz, announced the attack, which came amid Israeli strikes elsewhere in Tehran. Video footage verified by The New York Times shows an explosion at the main entrance to the prison compound and damage after a blast near a second entrance.

It was unclear why Israel struck the entrances to the prison. There were no immediate reports of injuries, and Iran said it still had control of the facility.

Here’s what to know about the prison and the Israeli attack:

What is Evin prison?

Thousands of prisoners are held at Evin, among them hundreds of dissidents, including prominent opposition politicians, activists, lawyers, journalists, environmental activists and students. It is also used to hold prominent non-Iranian or dual-citizen prisoners, many of whom have been accused of spying.

The prison sits on a hilltop in northern Tehran at the foot of the Alborz Mountains. The compound is surrounded by electrified barbed-wire fences as well as a minefield.

How was the prison damaged?

Several strikes targeted two entrances to the prison complex. IRNA, the Iranian state news agency, reported that projectiles had caused “damage to parts of the facility” but said the prison was “under full control.”