The twin car-and-suicide bombings Saturday night near the Besiktas stadium enraged top officials, including President Recep Tayyip Erdogan, who vowed to hunt down the perpetrators. The attack was the latest large-scale assault to traumatize a nation confronting an array of security threats.
PHOTOS: Blasts kill dozens in Istanbul
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The attack targeted police officers, killing 30 of them along with seven civilians and an unidentified person, Turkish Interior Minister Suleyman Soylu told reporters Sunday. He said 13 people had been arrested in connection with the "terrorist attack" and that authorities had some insight into how and when it was planned.
There was no immediate claim of responsibility for the attack but three senior officials said suspicions focused on Kurdish militants.
Deputy Prime Minister Numan Kurtulmus told the private news channel CNN Turk that "arrows point to the PKK," the outlawed Kurdistan Workers' Party, which has waged a decades-long insurgency. That assessment was echoed by Erdogan and Soylu.
"Our friends' evaluations suggest that the PKK was the perpetrator. There is a framework as to how the act was planned, when it was planned and how it was executed," Soylu said, declining to disclose details for fear of compromising the investigation.
In a furious address Sunday at a funeral for police officers killed in Saturday's attack, Soylu slammed Kurdish rebels and their allies in the West, referring to the PKK as "animals."
"Have you accomplished anything beyond being the servants, pawns and hit men of certain dark forces, of your dark Western partners?" he asked.
The PKK has waged a decades-long insurgency against the Turkish state, a battle that has resulted in the deaths of tens of thousands of citizens. Turkish officials frequently accuse the West of directly and indirectly supporting the Kurdish insurgency and of interfering in Ankara's fight against terrorism.
Erdogan vowed his country would fight "the curse of terrorism till the end" after paying a visit to some of the wounded at Haseki Hospital in Istanbul.
Surrounded by a crowd of people chanting his name and "God is greatest," Erdogan vowed that the perpetrators would not get away and would be forced to "pay an even heavier price."
The private NTV channel broadcast images of more than a 100 flag-carrying demonstrators marching along Istanbul's coastline toward the stadium at the heart of the blast area. Flags flew at half-staff Sunday across the country and at Turkey's foreign missions.
The first and larger explosion took place about 10:30 p.m. Saturday after the home team Besiktas beat visitor Bursaspor 2-1 in the Turkish Super League. Erdogan said the timing of the attack aimed to maximize the loss of life.
Soylu said the first explosion was caused by a passing vehicle that detonated in an area where police special forces were located at the stadium exit. A riot police bus appears to have been the target.
Moment later, a person who had been stopped in nearby Macka Park committed suicide by triggering explosives, according to the minister.
Soylu said 136 people remained hospitalized Sunday after the attack, including 14 under intensive care.
Forensic experts in white uniforms worked overnight, scouring the vicinity of the stadium and the vast park where the suicide bombing took place. Glass from the blown-out windows of nearby buildings littered the pavement.
Authorities have determined that up to 400 kilograms (880 pounds) of explosives were used in the attack, Kurtulmus told CNN Turk.
Vehicle and pedestrian traffic tentatively resumed Sunday in the blast area, which municipal workers rushed to clean up.
At noon, to the mournful sound of trumpets, funeral services were held at Istanbul's police headquarters for some of the slain police officers with the country's top brass in attendance. Their comrades solemnly carried the coffins, which were draped in the Turkish flag, as mourners wept.
This year Istanbul has witnessed a spate of attacks attributed by authorities to the Islamic State group or claimed by Kurdish militants. A state of emergency is in force following a failed July 15 coup attempt and the resulting government crackdown on alleged coup sympathizers has landed thousands in jail and forced tens of thousands of people from their jobs.
Saturday's incident marked one of the bloodiest to hit the bustling city at the crossroads of Europe and Asia. A triple suicide-and-gun attack on the city's Ataturk Airport in June killed 44 people and wounded scores of others. Kurdish-linked militants have claimed other deadly attacks in Ankara, Istanbul and areas of the southeast.
The steady stream of violence has delivered a bitter blow to Turkey's tourism sector, a mainstay of the country's economy.
Turkey is a partner in the U.S.-led coalition against the Islamic State and its armed forces are active in neighboring Syria and Iraq. It is also facing a renewed conflict with an outlawed Kurdish movement in the southeast.
Condemnations of the attack came from a range of Turkish politicians, from sports organizations like Besiktas, Bursaspor and UEFA, and from U.S., EU and Israeli officials.
Turkey's pro-Kurdish People Democratic Party, or HDP, issued a statement "strongly condemning" the attacks and saying it "felt great sadness and shared in the sorrow."
Turkish authorities have routinely accused the party of being linked to the PKK and backing terrorism. The party, which had both of its leaders detained in terror probes and multiple elected officials arrested or removed from public service in the southeast, denies the charge.
The chair of the main opposition Republican People's Party also condemned the attack.
Ned Price, a spokesman for the White House National Security Council, said Washington condemned the attack in "the strongest terms."
"Violence has no place in a democratic society," European Union Enlargement Commissioner Johannes Hahn wrote on Twitter.
Israeli Prime Minister Benjamin Netanyahu said at his Cabinet meeting Sunday that "Israel condemns any terror in Turkey, and Israel expects Turkey to condemn any act of terror in Israel. The battle against terror must be mutual."
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