Four more people have been detained in connection with two car bomb attacks that killed dozens in a Turkish town near the Syrian border, bringing the number of suspects in custody to 13, Turkey's prime minister said Tuesday.

Syria continued to reject Turkey's contention it was involved, condemning the attacks and offering to conduct a joint investigation into an attack it has blamed on Turkey itself.

Police were still searching for six other wanted suspects, Prime Minister Recep Tayyip Erdogan said. Turkish authorities have blamed the attack on a Marxist group with alleged links to the Syrian intelligence agency, but have not named the group.

Erdogan said the death toll on Tuesday stood at 51 people, including five Syrians. Saturday's powerful bombings were the deadliest in Turkey in years, shattering the border town of Reyhanli, a main hub for Syrian refugees and rebels fighting against Syrian President Bashar Assad's regime.

A statement carried by Syrian state television following a Cabinet meeting in Damascus put the blame on Turkey and its support for the rebels.

"Accusing the Syrian state of these cowardly and terrorist acts is totally baseless," the statement said.

It added: "The Turkish government is responsible for the situation in the border areas through turning them into a haven and passage for the terrorists and allowing gunmen to use the Turkish lands to commit crimes against the Syrians."

Once a close ally of Syria, Turkey turned into one of the Assad regime's harshest critics. It is a key supporter of the Syrian rebels, offering shelter for many senior and lower-ranking defected Syrian soldiers.

Syria's Information Minister Omran al-Zoubi said later that Erdogan's government was "taking political advantage of Reyhanli's bombings."

He said Syria would be willing to take part in a "joint and transparent investigation by special agencies in both countries."

There was no immediate response to the offer by Turkey, which has rejected a previous denial by Syria as a lie.

Turkish Interior Minister Muammer Guler said those detained were still being questioned and that authorities were looking for more suspects, including four people who may have been involved in planning the attack and two people suspected of "aiding and abetting" the attackers.

The attacks have sparked speculation that Turkey would be drawn into its neighbor's civil war, but Erdogan reiterated that Turkey would act with restraint.

"Thank God we are powerful, determined and experienced enough to make the culprits pay," Erdogan said. "However, we will act in a cool-headed manner and take steps with the reflexes of a great state."

He said investigators are also looking into whether security authorities were negligent.


Associated Press writers Albert Aji in Damascus and Bassem Mroue in Beirut contributed.