Reports said some of the vehicles that remain in Bangkok are from the 2nd Infantry Division in Prachin Buri province.
An army source reportedly said that Gen Prayuth Chan-ocha, the army chief, wanted the vehicles to remain at the 11th Infantry Regiment in the city.
Army spokesman Col Winthai Suwari admitted that some BTR-3E1 armoured vehicles were still in the capital. He said the vehicles had been held back for other units to study and use for training purposes.
The matter would be explained further at a later date, he said.
The BTR-3s are armoured personnel carriers with mounted guns. Thailand bought more than 200 of them from Ukraine, according to reports.