Defence Minister Sukumpol Suwanatat vows to press ahead with efforts to strip the opposition leader of his military rank.
He believes Abhisit Vejjajiva dodged mandatory conscription and used a falsified document to apply for an army position as a young man.
ACM Sukumpol said the Council of State had sent its opinion on the issue back to the Defence Ministry, but he would not let the matter rest. "The issue needs to be pushed forward to the end. We can't ignore it," he said.
As a former teacher at the army academy, Mr Abhisit has a rank of acting sub-lieutenant and received a salary from the academy.
A Defence Ministry source said the Council of State, the government's legal arm, replied that the defence minister has authority to take action. The minister has set up a committee to look into the matter and the Judge Advocate General is in charge of the study.
Earlier, the Office of the Ombudsman received a complaint on claims Mr Abhisit dodged conscription, and the office advised the Defence Ministry to act.
ACM Sukumpol earlier said Mr Abhisit had presented a falsified military personnel registration document to apply for a job as a lecturer at the Chulachomklao Royal Military Academy. The job reportedly allowed Mr Abhisit to be exempted from conscription.