Photo: AP

At least 11 people were killed and 36 others wounded in a rush-hour bombing in Istanbul on Tuesday, the Associated Press reports. The car bomb targeted a bus carrying riot police.

Istanbul governor Vasip Sahin said that seven police officers and four civilians were killed. Three of the wounded were in serious condition. No one has yet claimed responsibility for the attack—Istanbul’s fourth major bombing in a year. The New York Times reports:

Militants from the Kurdistan Workers’ Party, or P.K.K., which has carried out an insurgency against the Turkish state for more than three decades, have claimed responsibility for similar attacks against Turkish security forces since the breakdown last July of a fragile peace process.

A militant group with links to the Kurdish organization claimed responsibility for two major attacks this year in the capital, Ankara, that struck a military convoy and civilians, killing dozens.

Violence has surged in the country’s predominately Kurdish southeast in recent months, after a major military operation to eradicate militants from their strongholds in the region.

Tuesday’s attack took place on the second day of the holy Muslim month of Ramadan.