Turkey accused a group loyal to Syrian President Bashar al-Assad on Sunday of carrying out car bombings that killed 46 people in a Turkish border town and said the risk of unrest spreading to Syria's neighbours was increasing.
The twin car bombs, which ripped into crowded shopping streets in Reyhanli on Saturday, increased fears that Syria's civil war is dragging in neighbouring states despite renewed diplomatic moves to end two years of conflict that have killed more than 70,000. Foreign Minister Ahmet Davutoglu said it was time for the international community to take action against Assad.
"It is time for the international community to act together against this regime. We, like Jordan, are hosting hundreds of thousands of Syrians. Security risks to neighbouring countries are rising," he told a news conference during a visit to Berlin.
Authorities have arrested nine people, all Turkish citizens and including the alleged mastermind, deputy prime minister Besir Atalay told reporters.
Davutoglu said those involved were from an "old Marxist terrorist organisation" with direct links to the Assad regime. He said earlier that the Reyhanli bombers were believed to be from the same group that carried out an attack on the Syrian coastal town of Banias a week ago in which at least 62 people were killed.
Syrian Information Minister Omran Zubi denied any Syrian involvement and rejected what he called "unfounded accusations".
The conflict has fuelled a confrontation between Sunni and Shi'ite Muslims in the Middle East, with Shi'ite Iran supporting Assad, and Sunni powers like Saudi Arabia backing the rebels.
Banias is a Sunni pocket in the midst of a large Alawite enclave on Syria's Mediterranean coast. Activists in the area accuse militias loyal to Assad, an Alawite, of ethnic attacks. Reyhanli, home to thousands of Syrian refugees, is also predominantly Sunni and ethnic Arab and has become a logistics base for the rebels fighting Assad just over the border.
As the conflict has dragged on, local people have grown increasingly resentful over stretched economic resources and the violence being brought to their door.
Protests erupted in Reyhanli after the blasts, with some blaming Syrian residents and smashing Syrian car windows, and others railing against Turkey's foreign policy.
"We don't want the Syrians here any more. They can't stay here. Whether we even wanted them or not, they can't stay after this," said a teacher in Reyhanli, who gave his name as Mustafa.
He said the government's Syria policy was to blame.
"It's Tayyip Erdogan's politics that have done this. Turkey should never have got involved in this mess. We have a 900 km border with Syria. They come and go in wherever they like. Everyone here is in fear."
Interior Minister Muammer Guler said the car bombings - the deadliest incident on Turkish soil since Syria's war began - had been carried out by a group known to the Turkish authorities and with direct links to Syria's Mukhabarat intelligence agency.
The bombs scattered concrete blocks and smashed cars as far as three streets away. Among the dead were 35 Turks and three Syrians, Atalay said. Zubi, speaking on Syrian state TV, held Turkey responsible for the bloodshed in Syria by aiding al Qaeda-led rebels. He denied any involvement by Damascus in the bombings.
"Syria did not and will never do such a act because our values do not allow this. It is not anyone's right to hurl unfounded accusations," he said.
Nato-member Turkey has fired back at Syrian government forces when mortars have landed on its soil but despite its strong words has appeared reluctant to bring its considerable military might to bear in the conflict.
The bombings took place as prospects appeared to improve this week for diplomacy to try to end the war after Moscow and Washington announced a joint effort to bring government and rebels to an international conference. Turkey is hosting more than 300,000 refugees but is not alone in fearing the impact of Syria's war, which is helping inflame the Middle East's tangle of sectarian, religious and nationalist struggles.