Two female militants were killed by police when they fired shots and threw a grenade at a Turkish police bus in Istanbul on Thursday, local media and the Istanbul governor said.

Two police officers were lightly wounded in the attack, Governor Vasip Sahin told reporters in televised comments. An investigation was under way to identify the militant group responsible, he said.

One of the women threw a grenade and the other opened fire with what appeared to be a machine gun as the riot police bus drove towards the entrance of a police station in the Bayrampasa district of Turkey’s biggest city, footage from Dogan News Agency showed.

Police fired back, injuring one of the women, before tracking them to a nearby building, CNN Turk said.
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Special forces units and police surrounded the building, television footage showed, leading to an hour-long stand-off between the women and the police in which there was sporadic gunfire.

Attacks on Turkey’s security forces have increased as violence flares in the predominantly Kurdish southeast, where a ceasefire between Kurdistan Workers’ Party (PKK) militants and the state collapsed last July.

The PKK, considered a terrorist group by Turkey, the United States and the European Union, launched a separatist armed rebellion against Turkey more than three decades ago. More than 40,000 people, mostly Kurds, have since been killed.

Turkey has also become a target for Islamic State militants, who are blamed for three suicide bombings – one last year in the town of Suruc near the Syrian border and another in the capital, Ankara, and one in Istanbul in January. Those attacks killed more than 140 people.

There was no immediate claim of responsibility for Thursday’s attack. The radical leftist group DHKP-C has repeatedly staged similar attacks on police stations, largely in Istanbul suburbs.

A suicide car bombing targeted military buses in Ankara killed 29 people last month. The government said that attack was carried out by a member of YPG, the Syrian Kurdish militia, with help from PKK militants.