Eleven people, including seven police force members, were killed Tuesday in a car bombing in Istanbul near a historic area popular with tourists, the local governor said.
Governor Vasip Sahin also reported 36 injured, including three in serious condition. The bomb was placed in a parked car and apparently remotely detonated as a police bus was passing.
The morning attack took place less than 1 kilometre from the Grand Bazaar, a popular tourist site in the Vezneciler area, near a public transport station.
Shops, cars and a hotel near the explosion point were damaged in the attack. Windows of the 16th century Sehzade Mosque were blown out and some stone fixtures destroyed.
The police bus itself was blackened and crumpled by the explosion. A heavy police force remained in the area.
President Recep Tayyip Erdogan vowed to fight against terrorism until the "Day of Resurrection" and said efforts were focused on reducing the threat posed to the country.
"We will fearlessly and tirelessly continue our fight against these terrorists, until the end," Erdogan said after visiting a hospital where injured people were being treated. The attack "cannot be forgiven," he said.
This was the third major attack in Istanbul this year. There were also two deadly car bombings in the capital, Ankara.
Turkey's tourism industry has been tanking amid the threats, with the number of foreign visitors last month plummeting by 28 per cent, compared to the same period last year. A diplomatic row with Russia has also hurt.
Police arrested four people in connection with the attack, which was said to have been carried out using a rental car, the Dogan news agency reported.
The United States and European Union condemned the attack in separate messages.
A Turkish court imposed a partial ban on media publicizing information related to the bombing, the broadcasting authority (RTUK) reported.
Such bans, common after attacks in the country's main cities, normally prohibit broadcasting unofficial information, including that about ongoing investigations, and some images from the scenes of the attacks.
The bombing comes during the first days of Ramadan, the Islamic holy month.
Istanbul had already been hit by two major bombings this year, including in tourist areas. Both attacks were blamed on Islamic State.
Kurdish militants from the shadowy Kurdistan Freedom Falcons (TAK) faction claimed two car bombing attacks in Ankara this year and a suicide bombing in Bursa.
The country is facing unrest with the banned Kurdistan Workers' Party (PKK) and affiliated fighters in the mostly-Kurdish south-east, leaving many hundreds dead, including militants, security forces and civilians. About half a million people have been displaced.
A peace process and ceasefire collapsed last year between the Kurdish militants and the state.