Maj Gen Apirat, who is responsible for overseeing the overall military operation as well as coordinating with the Centre for the Administration of Peace and Order (Capo), said the incident took place at 9.10pm.
The two soldiers who were shot and wounded were Chief Warrant Office Chaiyan Lekpong and L/Cpl Prasert Chansri.
They were admitted to Ramathibodi Hospital.
"Our soldiers have filed a police complaint that plaincloth soldiers on motorcycle patrol were fired at, possibly by NSPRT guards providing security around their rally site. They might have shot the soldiers out of a misunderstanding. However, we have to take legal action against them because the protesters should not have been armed.
"After the incident, I have ordered the setting up of more checkpoints," Maj Gen Apirat said.
CWO Pairoj Kantha, one of five plainclothes soldiers who were patrolling on three motorcycles, told a police officer on duty that the two soldiers who were wounded were riding on the first motorcycle and he was riding on the second.
At the time of the incident, he heard one gunshot, which was followed by a series of gun shots fired from a war weapon, possibly an AK47 rifle.
The first motorcycle fell in the soi by Wat Benjamabopit School connected to Si Ayutthaya road.
"When the first motorcycle fell, two NSPRT guards came out of a bunker. One of them pointed at the head of a wounded soldier with a .38 revolver. I had to quickly identiy myself as a soldier on patrol. The guard pulled back his weapon. I immediately arranged for the wounded to be admitted to hospital," CWO Pairoj said.