Officials say three of those killed were Turkish and the rest were Syrians.
Turkey’s NTV news channel says the blast occurred Monday on Turkish soil, about 40 meters from the Cilvegozu border crossing in the southern province of Hatay.
Deputy Prime Minister Bulent Arinc said authorities are investigating all possible causes for the blast.
Several reports are quoting local mayor Huseyin Sanverdi as saying a Syrian-registered car is believed to have been at the center of the blast.
The border area between the two countries has been the scene of fighting between rebels and Syrian President Bashar al-Assad’s military forces.
“The blast came amid fresh reports of rebel gains in several parts of Syria. It was unclear, however, whether the explosion was deliberate, and Turkish officials said an investigation was continuing into the cause and circumstances of the blast, which coincided with heightened Turkish concerns about the risk that the violence raging across the border in Syria would spill over into Turkey.
Turkish Deputy Prime Minister Bulent Arinc told reporters in Ankara that a van with Syrian license plates driving into Turkey from Syria had exploded just before the Turkish checkpoint at the Cilvegozu border crossing near Reyhanli, in Turkey’s Hatay province.