The two soldiers are identified as Sgt Phitsanu Phuangrung and L/C Natthawut Cherdsungnern of the 31st Infantry Regiment's 2nd Infantry Battalion in the central province of Lop Buri.
Deputy Metropolitan Police chief Pol Maj-Gen Charnthep Sesavech said the pair were detained at 23.30pm and brought in for further investigation.
Police searched the men's pickup truck and found one M16 rifle with 1,976 rounds of ammunition, an 11mm pistol, two teargas canisters, some additional fiearms magazines, a knuckle-duster and a pocket knife. The police brought them for questioning at Lumpini Police Station after the men failed to show them an authorised firearms transfer certificate.
Police said the two soldiers refused to speak to the police and will be charged with possessing firearms and ammunition without authorised permission as well as carrying firearms and ammunition into the city. The staff judge advocate will be asked to take them for further action under the military court procedures.
Maj Gen Vara Boonyasit, 1st Infantry Division commander, pledged to let justice run its course and that he would not protect any soldiers found committing any wrongdoing. The army's staff judge advocate will participate in the police investigation to determine whether the pair were hired to carry the weapons which did not belong to his unit.