TAK claimed responsibility on its website Sunday for the previous night's two bomb blasts outside the stadium of the Besiktas football club that left 38 people dead and 155 wounded.

The Kurdish splinter group, which took responsibility for other attacks in Turkey earlier this year, said two of its members had died in Saturday's assault.

Turkish authorities said up to 400 kilograms of explosives had detonated in the attackers' car. The other blast had been carried out by a suicide attacker, they said.

Government vows 'revenge'

Erdogan said in a published statement that those behind the attack would "pay a heavier price" for Saturday evening's attack, which adds to an array of events traumatizing the Turkish nation.

Attending a funeral Sunday for five victims, Interior Minister Suleyman Soylu told mourners: "Sooner or later we will have our revenge."

Soylu said 30 police officers, seven civilians and one person yet to be identified were killed by the blasts.

Forensic experts spent Sunday collecting evidence outside the stadium and the nearby Marca park, where the suicide bomber struck at about 10.30 p.m.

Besiktas had just beaten visitor Bursaspor 2:1 in a Turkish Super League match.

On Sunday, thousands of people marched around the stadium. Some also laid flowers outside the stadium. Many shouted "Down with the PKK!" and "Our homeland is indivisible!"

Besiktas vowed to "stand firm around the vile attackers" and Turkey's constitutional court condemned what it termed "the nefarious terrorist attack."

Prime Minister Binali Yildirim's office ordered flags to be flown at half-mast across the country and at Turkey's foreign missions on Sunday.

Pro-Kurdish party condemns bombing

The central committee of Turkey's pro-Kurdish People's Democratic Party, or HDP, issued a statement "strongly condemning" the attacks and saying it "felt great sadness and shared in the sorrow."

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 remains in force following July's failed coup attempt.

A subsequent government crackdown on alleged coup sympathizers has landed thousands in jail and forced tens of thousands of people from their jobs.

Vehicle and pedestrian traffic tentatively resumed Sunday in the stadium precinct, which municipal workers rushed to clean up.

ipj/sms (AFP, AP, dpa)