A blast at an outdoor wedding party in the south Turkish city of Gaziantep has killed at least 30 people and injured 94 more, the authorities say.
President Recep Tayyip Erdogan said so-called Islamic State, IS, was likely to have carried it out amid reports of a suicide bomber targeting the party.
The attack, in an area popular with university students, could be heard across the city.
Gaziantep, near the Syrian border, is known to have several IS cells.
Reports said the city was already on edge before the attack because of events in Syria, where IS has been battling Syrian Kurdish forces.
A suicide bomber believed to have links to IS killed two policemen in Gaziantep in May.
Turkey has been hit by a series of bombs both by IS and Kurdish militants in the past year. The last IS attack, on Istanbul airport in June, killed more than 40 people.
The jihadists have recently lost ground in northern Syria, including a former stronghold, Manbij. Syrian rebel soldiers are preparing to advance further into the IS-held province of Jarablus.
If this bomb was the work of IS, there will be speculation it was a revenge attack, intended as a show.
According to the reports, the bomb went off in a part of town with a large Kurdish community and there seem to have been many Kurds at the wedding.
In a written statement published by local media in Turkish, Mr Erdogan argued there was “no difference” between IS, the Kurdish militants of the PKK, and followers of US-based cleric Fethullah Gulen, whom he blames for the coup attempt last month.
“Our country and our nation have again only one message to those who attack us – you will not succeed!” he said.
On Saturday, Turkey’s government said the country would take a more active role in efforts to end the war in Syria.
Prime Minister Binali Yildirim said a future political settlement for Syria must not include President Bashar al-Assad, IS or Turkey’s own Kurdish separatist rebels,
“In the six months ahead of us, we shall be playing a more active role,” Mr Yildirim said. “It means not allowing Syria to be divided along ethnic lines.”