ISTANBUL—Turkey’s president blamed Islamic State for turning a youth into a human bomb at a crowded outdoor wedding party in southeast Turkey’s largest city, killing at least 51 people in a weekend attack that underscored how the war in neighboring Syria is destabilizing the region.

The bombing in Gaziantep targeted a largely Kurdish neighborhood and turned a celebratory summer evening into a scene of anguish and mourning, as the couple recovered on Sunday from injuries sustained in the massive Saturday blast and investigators worked to identify the charred body parts of guests and family members.

Dozens of funerals took place on Sunday, including ceremonies for 29 children who forensics teams had managed to identify. Nearly 100 people, including many women and children, were wounded in the attack.

There was no immediate claim of responsibility, but President Recep Tayyip Erdogan said a youth between the ages of 12 and 14 carried out the attack and said the bombing had the hallmarks of Islamic State.

Turkey has been battling the terror group as part of the international coalition, and has suffered multiple bombings targeting Turkish citizens already this year, including a devastating attack at Istanbul’s Atatürk International Airport.