A midday explosion in Turkey's southeastern city of Suruc near the Syrian border killed 28 people Monday and sent nearly 100 others to the hospital, Turkish officials said.
The prime minister's office gave the casualty toll in a phone call to The Associated Press.
Television footage showed bodies lying beneath trees outside the building in the mostly Kurdish town, some 10 kilometres from the Syrian town of Kobani, where Kurdish fighters have been battling Islamic State.
"I saw more than 20 bodies. I think the number of wounded is more than 50. They are still being put into ambulances," one witness told Reuters by telephone, giving his name as Mehmet. "It was a huge explosion, we all shook."
There was no immediate claim of responsibility for the blast.
"Our initial evidence shows that this was a suicide attack by Islamic State," one senior official in Ankara told Reuters.
A second official also said Islamic State appeared to have been responsible and that the attack was a "retaliation for the Turkish government's efforts to fight terrorism".
A Turkish official told the Assicoated Press that authorities have evidence the attack was a suicide bombing and suspect the Islamic State group was behind it. He spoke on condition of anonymity because he was not authorized to speak on the record.
Suruc has been the scene of fierce battles between Kurdish groups and the Islamic State group. Kobani was the Islamic State group's biggest defeat last year since the militants established control over large swathes of Iraq and Syria, and has become a symbol of Kurdish resistance.
A second bomb went off Monday south of Kobani near a Kurdish militia checkpoint on the road to Syria's largest city of Aleppo, according to Idriss Naasan, a Kurdish official in Kobani. It caused minor damage and no casualties, he said.
The private Turkish news agency DHA said the blast in Suruc occurred at a cultural centre while a political group was holding a news conference on Kobani's reconstruction. News reports said 300 people from the Federation of Socialist Youths were staying at the centre and were preparing to travel to Kobani to help with the rebuilding.
Suruc hosts the largest refugee camp in Turkey, which has seen nearly two million Syrians cross its border to flee the fighting in their homeland.
More than 220,000 people have been killed and at least a million wounded since Syria's crisis began in March 2011, according to the U.N.
Kobani was also the scene of surprise IS attacks last month that killed more than 200 people.