Twelve people were killed on Monday at one of the main crossing points for Syrian refugees into Turkey.
A Syrian minibus exploded killing three Turks and nine Syrians.
At least 28 other people were wounded, 13 of them seriously.
Deputy Prime Minister Bulent Arinc said the minibus exploded as it was driving through a stretch of no-man's land between the two countries.
He said the government was investigating all possible causes, but it was wrong to jump to hasty conclusions.
Three other ministers were to fly to the area later in the day to be briefed on the incident.
NTV reported the explosion happened 40 metres from the Cilvegozu crossing.