Turkey captured a key suspect in an attack five years ago that killed dozens of people, and he alleged the twin bombings were orchestrated by Syrian intelligence.
Yusuf Nazik confessed his role in the 2013 car bombings in the border town of Reyhanli that killed 53 people. According to media reports, the 34-year-old accused Syria's Mukhabarat spy agency of plotting the attack.
He was seized in the Syrian city of Latakia - the heartland of President Bashar al-Assad's support - in a "pinpoint operation" by Turkey's National Intelligence Organisation, the Anadolu news agency reported.
In a video released on Wednesday by the Turkish government, Nazik appeared in a blue tracksuit top and jeans next to a Turkish flag. He called on other suspects to surrender and warned Turkey would hold the Assad government to account for the attack.
"I was not able to escape from the Turkish state," he said in the video.
"I am calling out to my friends in Syria, turn back while there still is time. The Turkish state will protect us. I am calling out to the state of Syria, the Turkish state will make you pay eventually."
The attack on May 11, 2013, saw one car bomb detonated outside council offices leave a massive crater in the ground and destroy nearby buildings.
A second vehicle-bomb blew up a few minutes later less than a kilometre away outside a post office.
Most of the casualties were Turks but Syrian refugees were also killed just a couple of kilometres from the Syrian border.
Nazik, a Turkish citizen from nearby Antakya, had been one of several suspects wanted in connection to the attack. Turkey's intelligence agency, known as MIT, reportedly carried out the operation to capture him. No details on when it took place were released.
Nazik admitted scouting targets, transporting the explosives from Syria to Turkey, as well as procuring and loading the vehicles used in the bombing. He identified his Syrian contact as an intelligence officer named Mohammed who went by the codename, Hadji.
"We take the information provided by Yusuf Nazik about the involvement of Syrian intelligence operatives in the 2013 Reyhanli attack very seriously," a senior Turkish official told Al Jazeera on condition of anonymity.
"His testimony corroborates long-standing rumours about the Assad regime's active role in the bombing, which killed 53 innocent people. Nazik's capture and repatriation should serve as a reminder to all other criminals that we will never stop hunting them. We will spare no effort to find you, catch you, and bring you to justice."
Justice Minister Abdulhamit Gul praised the operation. "Our state will come after every kind of terrorist group and our independent judiciary will deliver fair punishment, wherever the culprit may be," he told reporters.
In February, a court in Ankara handed down life sentences against nine people involved in the Reyhanli attack. Thirteen others received prison terms of up to 15 years.