The vehicle was in a convoy of more than 10 armoured personnel carriers (APCs) travelling from a military camp in Chonburi province towards the border with Cambodia, a military source said.
The accident took place at about 4am after the driver of an APC lost control of the vehicle. It swerved across the ditch dividing the highway it was on and came to a stop on the other side, partially blocking oncoming traffic.
Six soldiers were injured. Three were sent to hospital while the others suffered only minor injuries.
All vehicles in the convoy carried banners saying “For Training”.
The military source said that 20 vehicles from a military camp in Chonburi were driving to areas near the border with Cambodia in Prachin Buri and Sa Kaeo provinces.
The convoy had no link to politics, said the source, implying that preparations for a military coup were not underway.