ANKARA, Turkey -- Nine Turkish citizens believed to have links to the Syrian intelligence agency have been detained in connection with twin car bombings that shattered a Turkish border town, officials said Sunday, as Syria rejected allegations it was behind one of the deadliest attacks in Turkey in years.

The bombings left 46 people dead and marked the biggest incident of violence across the border since the start of Syria's bloody civil war, raising fears of Turkey being pulled deeper into the conflict.

Harsh accusations from both sides signalled a sharp escalation of already high tensions between the two former allies, with Turkey vowing a strong response and Syria branding Turkey's prime minister "a butcher."

"This incident was carried out by an organization ... which is in close contact to pro-regime groups in Syria and I say this very clearly, with the Syrian mukhabarat," said Turkish Interior Minister Muammer Guler. He did not name the organization.

Among the nine people detained overnight was the mastermind of the attack and more were expected, Guler said.

"We have determined that some of them were involved in the planning, in the exploration and in the hiding of the vehicles," he said.

Deputy Prime Minister Besir Atalay said Turkish authorities determined that the nine were involved through their "testimonies and confessions," but did not elaborate during a joint press conference in Hatay, near the border town of Reyhanli where the bombs struck.

Saturday's twin bombings fifteen minutes apart damaged some 850 buildings in the town, a hub for Syrian refugees and rebels just across the border from Syria's Idlib province. It also wounded dozens of people, including 50 who remained hospitalized Sunday.

Syria and Turkey became adversaries early on during the uprising against Syrian President Bashar Assad that erupted in March 2011. Since then, Turkey has firmly sided with the Syrian opposition, hosting its leaders along with rebel commanders and providing refuge to hundreds of thousands of Syrian refugees.

Authorities had so far identified 35 of the dead, three of them Syrians. Families began burying their loved ones in funerals on Sunday.

Earlier in Damascus, Syrian Information Minister Omran al-Zoubi rejected Turkey's charges that Assad's regime was behind the bombs.

"Syria didn't and will never undertake such acts because our values don't allow us to do this," al-Zoubi told a news conference.

He accused Turkey of destabilizing the border areas between the two countries by supporting the rebels, who the regime has labeled terrorists.

"They turned houses of civilian Turks, their farms, their property into a centre and passageway for terrorist groups from all over the world," Al-Zoubi said. "They facilitated and still are the passage of weapons and explosives and money and murders to Syria."

Al-Zoubi also branded Turkish Prime Minister Recep Tayyip Erdogan a "killer and a butcher," adding that the Turkish leader "has no right to build his glory on the blood of the Turkish and Syrian people."

Tensions had earlier flared between the Syrian regime and Turkey after shells fired from Syria landed on the Turkish side, killing five Turks, and prompting Germany, the Netherlands and the U.S. to send two batteries of Patriot air defence missiles each to protect their NATO ally.

Speaking to Turkish reporters in Berlin late Saturday, Ahmet Davutoglu said his country would hold those responsible for the bombings but had no immediate plans to involve its NATO allies.

After publicly pointing the finger publicly at Damascus, Turkey will likely have to respond to such a brazen violation of its sovereignty -- again raising the risk of a regional war, just a little over a week after Israel escalated its role in the Syria conflict by striking suspected shipments of advanced Iranian weapons in Syria.

Erdogan is flying to the U.S. for talks with President Barack Obama next week. In the wake of the car bombs, both men could come under greater pressure to take action.

"It comes down to an existential struggle," said Salman Shaikh, director of the Brookings Doha centre. "Those who oppose Assad really have to show that they mean it now."

The U.S. has provided humanitarian aid to the Syrian opposition, but has been reluctant to provide military aid, in part because al-Qaida-linked militants are becoming increasingly influential in the armed opposition.

Last week, Erdogan alleged that Syria has been using chemical weapons, delivering them on at least 200 missiles, though he provided no evidence. Syria has denied using chemical weapons.

Obama has portrayed the use of chemicals by the regime as a "red line" that would have harsh consequences, but has said he needs more time to investigate allegations..

In another potentially destabilizing element, Israel signalled last week that it will keep striking at shipments of advanced Iranian weapons that might be bound for Hezbollah. Syria has traditionally be a conduit for Iranian weapons to Hezbollah.

Earlier this month, Israel struck twice at what Israeli officials said were shipments of advanced Iranian missiles near Damascus. In response, Hezbollah chief Hassan Nasrallah said this week that Syria is expected to deliver "game-changing" weapons to his militia. If more than empty rhetoric, this would likely provoke more Israeli strikes.