At least 11 people were killed after a bomb exploded near a bus carrying riot police in Istanbul, Turkish media reported Tuesday.

The blast occurred near an Istanbul University building in the city’s busy Vezneciler district during the morning rush hour.

There was no immediate claim of responsibility. Several dozen people were injured.

Terrorism has been on the rise in Turkey recently. Militants killed more 60 people in bombings in Istanbul and Ankara in February and March.

The Kurdistan Workers’ Party, or PKK, rebels and the Islamic State have been behind a series of deadly bombings there.

The PKK is waging a war against Ankara for autonomy for Turkey’s Kurds in the southeast of the country. Its decades-long conflict against the Turkish state has claimed 40,000 lives.