Kurdistan Freedom Hawks, an armed group known by the Kurdish-language acronym TAK, has claimed responsibility for two explosions that have killed at least 38 people outside an Istanbul football stadium.
In a statement posted on its website on Sunday, the group, seen as a faction of the armed Kurdish group PKK, said two of its fighters also died in the attack that targeted police officers on Saturday evening outside Besiktas football stadium.
The attack left 160 people injured, including 19 who are in intensive care.
Turkey was observing a day of mourning on Sunday, with flags flown at half mast.
OPINION: Turkey's war on the PKK
President Recep Tayyip Erdogan called a security meeting on Sunday after declaring at the funeral in Istanbul of five of the slain 30 police officers that Turkey would "fight terrorism to the end" .
Binali Yildirim, Turkey's prime minister, who was at the funeral with Erdogan, earlier blamed the PKK for carrying out the blasts.
In June, TAK claimed responsibility for an attack that killed 11 people in Istanbul. Dozens of people were also killed by the group in the capital Ankara in February and March.
The group's founders are believed to have broken away several years ago from the PKK, which has waged an armed campaign against the Turkish state for more than three decades.
Suleyman Soylu, the Turkish interior minister, said on Sunday at least 13 people were detained while government prosecutors arrested three others for social media posts that "attempted to praise terrorism.
"Sooner or later, we will have our vengeance. This blood will not be left on the ground, no matter what the price, what the cost," Soylu, who also attended the Istanbul funeral, said.
Outside the Besikstas football stadium, people gathered to lay flowers, many holding Turkish flags and shouting: "Our homeland is indivisible."
Numan Kurtulmus, deputy prime minister, said at least 300-400kg of explosives had been used to target the police officers.
|At least 30 of the victims of Saturday's attack were police officers [Reuters]
In a statement, the Besiktas football team pledged to "stand firm against the vile attackers who will never achieve their goal".
The arena is across the Ottoman-era Dolmabahce Palace which also houses Yildirim's offices, and is about a kilometre from the busy Taksim Square, a magnet for tourists.
Video purporting to show the father of one of the victims, a 19-year-old medical student who had been in Istanbul for a weekend visit, went viral on social media in Turkey.
"I don't want my son to be a martyr. My son was massacred," the footage showed the father as saying.
"His goal was to be a doctor and help people like this, but now I am carrying him back in a funeral car."
Series of bombings
Turkey has been hit by a series of bombings this year, including five in Istanbul.
In June, 47 people were killed in a triple suicide bombing and gun attack at Istanbul's Ataturk airport, with authorities blaming the Islamic State of Iraq and the Levant (ISIL, also known as ISIS) group.
Another 57 people, including 34 children, were killed in August in a suicide attack by an ISIL-linked bomber at a Kurdish wedding in the southeastern city of Gaziantep.
The country is also still reeling from a failed July 15 coup blamed on the US-based preacher Fethullah Gulen which has been followed by a mass dismissal of his alleged supporters from state institutions.
Source: Al Jazeera and news agencies