The death toll in twin car bombings in a Turkish town near the Syrian border has increased to 51, the prime minister said on Tuesday.
"There are 48 wounded people in hospitals, seven of them are Syrian citizens, and 17 are in critical condition," Recep Tayyip Erdogan told his ruling party lawmakers in parliament.
He was speaking before his departure to Washington for talks with President Barack Obama, where he is expected to press for stronger US action against the Syrian regime.
Erdogan also confirmed that the number of suspects held by Turkish police had risen to 13.
The attacks in the town of Reyhanli were the deadliest since the start of an uprising against the regime in neighbouring Syria two years ago.
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Turkey has blamed a radical Marxist group affiliated with President Bashar al-Assad's regime for the attack. Damascus has denied the allegation.
The Turkish premier said the attack would not go unpunished.
"Sooner or later we'll make the perpetrators of this heinous attack pay a price," he said.
Turkey cut contact with former ally Damascus after its calls for a peaceful resolution of the conflict -- which is now in its third year and has left more than 80,000 people dead -- went unheeded.
Ankara has sided with the rebels fighting to topple Assad's regime and has taken in around 400,000 refugees as well as army defectors and repeatedly called on the international community to act on the unfolding crisis.
"We do not have a problem with the Syrian people, but with the heinous, brutal, tyrant dictator in Syria," said Erdogan.
The attacks also provoked a backlash against Syrian refugees in Turkey but government officials have repeatedly warned against provocations and said Turkey will maintain its open-door policy for Syrians fleeing the regime's crackdown.