ISTANBUL, TURKEY―In honor of the 38 people killed and 155 wounded on Saturday, December 10, Turkey has declared a national day of mourning. Along with the tribute, a full investigation by officials has been launched. The double explosions in Istanbul occurred near the Besiktas soccer stadium. The first bombing struck around 10:30 p.m. after the conclusion of the Turkish Super League game.

The explosion was caused by a vehicle that detonated near the stadium’s exit. Multiple police forces were stationed. A riot police bus was the target, says Turkish Interior Minister Suleyman Soylu. A person was then stopped moments later near the stadium at Macka Park, where they committed suicide by triggering another explosive device.

The Kurdistan Freedom Falcons (TAK), a Turkey-based Kurdish militant group, has taken responsibility for the attack. Via their website, TAK released a statement explaining that two of its members sacrificed themselves in the attack, targeting security officers outside the stadium shortly after the soccer match Saturday night. The posting indicated that the attack was for the ongoing imprisonment of the Kurdistan Workers’ Party (PKK) leader Abdullah Ocalan and was a retaliation for the state violence in the southeast. Authorities consider TAK to be a branch off of PKK. Kurdish militants have claimed other deadly attacks in Ankara, Istanbul and areas in southeast Turkey after waging a revolt against the state that has lasted decades.

This was the latest large-scale hit on a nation that is confronting numerous security threats. The two suicide bombings caused President Recep Tayyip Erdogan to promise the people of Turkey [he will find] the perpetrators and make them “pay a heavier price.”

The blasts targeted the police, killing 30 officers, seven civilians, and one unidentified person. Soylu told reporters Sunday that 13 people who are believed to be involved in the “terrorist attack” have already been arrested. The Interior Minister stated that the authorities had some insight on how and when it was planned.

“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,” said Soylu. He declined to detail the investigation for fear of compromise.

After visiting victims who were wounded from the bombings, President Erdogan promised his country would fight “the cause of terrorism till the end.”

Funeral services and ceremonies have been held for those killed in the attack. Hundreds of demonstrators marched along Istanbul’s coastline heading towards the stadium, the epicenter of the attack. Flowers were placed by civilians and officials alike around the outer edges of the soccer stadium.