ISTANBUL (AP) -- A rush-hour car bomb attack targeting a bus carrying riot police killed 11 people and wounded 36 others Tuesday, Istanbul's governor said.
Speaking at the scene of the blast in the district of Beyazit, Istanbul Governor Vasip Sahin said the dead included seven police officers and four civilians. At least three of the wounded were in serious condition.
The explosion was caused by a bomb placed inside a car and was detonated as the police vehicle was passing by, Sahin said.
The police bus was overturned from the force of the blast which also damaged nearby buildings, including a closed hotel whose entrance appeared gutted and windows were blown out. The blast also shattered windows at a famous 16th-century Ottoman mosque, Sehzadebasi, wrecked several cars and forced cancellation of exams at nearby building of Istanbul University.
President Recep Tayyip Erdogan visited some of the wounded at Istanbul's Haseki hospital, where two people were undergoing surgery.
"These (attacks) are being carried out against people whose duty it is to ensure the security of our people. These cannot be pardoned or forgiven. We shall continue our fight against terrorists tirelessly until the end," he told reporters outside the hospital.
Foreign Minister Mevlut Cavusoglu condemned the attack, which occurred on the second day of the holy Muslim month of Ramadan.
"They are cold-heartedly exploding bombs on a Ramadan day," Cavusoglu said in a television interview.
There was no immediate responsibility claim and Sahin would not comment on who may be behind the attack. Authorities imposed a news blackout preventing media from reporting details of the investigation.
U.S. Ambassador to Turkey John Bass issued a statement condemning the "heinous attack" and saying his country continues to "stand shoulder-to-shoulder with Turkey in the fight against terrorism."
Tuesday's attack was the fourth major bombing in Istanbul this year. Two of them targeting tourists and two hitting security forces. The spike in violence has led to a sharp dip in tourism, a mainstay of the economy.
Rebels of the Kurdistan Workers' Party, or PKK, have targeted police and military personnel since July, when a fragile peace process between the rebels and the government collapsed.
The Islamic State group has also been blamed for a series of deadly bombings in Turkey, which is part of the U.S.-led coalition against IS.
An estimated 500 Turkish security personnel have been killed in attacks or in conflict with the Kurdish rebels, according to the military, which claims to have killed 4,900 PKK militants in Turkey and northern Iraq. Turkish warplanes regularly raid PKK bases in northern Iraq.
Limited access to conflict areas in the southeast has made it difficult to verify casualty figures.
The PKK, considered a terrorist organization by Turkey and its allies, is fighting for autonomy for Turkey's Kurds in the southeast of the country. The decades-long conflict has claimed 40,000 lives.
Last month, eight people were wounded in Istanbul when a car bomb targeted a military vehicle.