Turkey now believes fighters loyal to Syrian President Bashar al-Assad were behind the devastating twin bombs that tore through the southern city of Reyhani, killing at least 43.
Syria has denied it but fears are growing inside Turkey that this attack drags them closer to war with their neighbour.
As investigators look for clues as to who is behind the blast, residents of Reyhanli say there is little doubt.
"It's obvious who did it," says this man, pointing to Syria.
One analyst says Turkey may well respond with force.
(SOUNDBITE) (Turkish) ANALYST ALI NIHAT OZCAN, SAYING:
"Turkey will ask the international community to put more pressure on Syria through diplomacy but at the same time I assume it will try to retaliate with an undercover operation."
The foreign minister said Turkey reserves the right to take "every kind of measure".
Turkey has long supported rebels engaged in a bitter civil war with Syria's government.
