ANKARA, Turkey - Turkey's prime minister vowed Sunday that his country wouldn't be drawn into Syria's civil war, despite twin car bombings the government believed were carried out by a group of Turks with close ties to pro-government groups in Syria.

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's being pulled deeper into a conflict that threatens to destabilize the region.

Syria has rejected allegations it was behind the attacks. But Turkish authorities said Sunday that they had detained nine Turkish citizens with links to the Syrian intelligence agency in connection with the bombings in the border town of Reyhanli, a hub for Syrian refugees and rebels just across from Syria's Idlib province.

Harsh accusations have flown between Turkey and Syria, signaling a sharp escalation of already high tensions between the two former allies. But Prime Minister Recep Tayyip Erdogan suggested that Turkey would not be drawn militarily in retaliation.

He insisted Turkey would "maintain our extreme cool-headedness in the face of efforts and provocations to drag us into the bloody quagmire."

"Those who target Turkey will be held to account sooner or later," he said. "Great states retaliate more powerfully, but when the time is right. ... We are taking our steps in a coolheaded manner."

Turkish Foreign Minister Ahmet Davutoglu told reporters in Berlin that those detained were linked to a Marxist terrorist group.

Sabah, a Turkish newspaper close to the government, reported Sunday that authorities suspect that the leader of a former Marxist group, Mirhac Ural, may have revived his group and ordered the attack.

The group, Acilciler, was one of many Marxist groups active in Turkey through the 1970s and 1980s, and was long-rumored to have been formed by the Syrian intelligence agency. Many of its militants allegedly included ethnic Arab Turks belonging to a sect close to Syria's Alawites.

"Some believe that now that relations [with Turkey] have deteriorated again, Syria may have reactivated the group to cause turmoil in Turkey," said Nihat Ali Ozcan, a terrorism expert at the Ankara-based Economic Policy Research Foundation of Turkey.

Guler said that a ringleader was among those detained and that more arrests were expected. "We have determined that some of them were involved in the planning."

Saturday's twin bombings 15 minutes apart damaged 735 businesses and 120 apartments, leaving smoking hulks of buildings and charred cars. 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 al-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.

On Sunday, hundreds of people marched in the city of Antakya, near Reyhanli, protesting the government for its Syria policies and support for the rebels - which some believe has exacerbated the conflict in Syria.