Turkish Prime Minister Recep Tayyip Erdogan on Tuesday firmly rejected a Syrian proposal to hold a joint probe over a twin car bomb attack that killed 51 people.
"The administration in power in Damascus is illegal ... how can we recognise a structure that isn't even recognised by its own citizens," Erdogan told reporters before leaving for a meeting with US President Barack Obama in Washington on Thursday.
Syria said earlier Tuesday it was willing to carry out a joint investigation with Turkey into the deadly attacks in the border town of Reyhanli that Ankara has accused Damascus of masterminding.
"If the government of (Prime Minister Recep Tayyip) Erdogan calls for a joint, transparent investigation by the two countries, we have no objection, in order to find the truth," Information Minister Omran al-Zohbi had said.
"The truth must be announced to the Syrian and Turkish people," he was quoted as saying by state media.
Saturday's twin car bombings also wounded dozens.
Turkish police have arrested 13 suspects.
Erdogan also announced his government would present a "road map" on the Syrian crisis after his return from the United States.
"We will come up with a road map after our talks and we will act in accordance," he said but did not give details.
Erdogan called his country "the first victim of the Syrian crisis in the region".
"We cannot just stand by watching what's happening," he added, bemoaning a lack of consensus at the UN Security Council on a resolution that would condemn Damascus.
Ankara has sided with the rebels fighting to topple the regime of Bashar al-Assad and has taken in around 400,000 refugees as well as army defectors, prompting a crisis in ties with the Syrian regime.
The crisis will be at the centre of Erdogan's talks with Obama.