There is a serious problem with discipline in the South African National Defence Force (SANDF), Defence and Military Veterans Minister Lindiwe Sisulu admitted on Tuesday.

"You're right, there is a problem of discipline... a serious problem of discipline in the defence force," she told members of Parliament's Defence and Military Veterans Portfolio Committee.

If there were not, "we wouldn't have had the problem we had on the lawns at the Union Buildings" two weeks ago.

Sisulu was briefing the committee on the violent, illegal protest by an estimated 2000 SANDF soldiers - members of the South African National Defence Union, some armed with knobkierries, pangas and petrol bombs - in Pretoria on August 26.

"Exactly what has been going round is concerning, and we're trying to get to the bottom of it. It is not something we are proud of. I don't think there is any South African out there who is proud of the discipline of the defence force."

Sisulu repeated that she stood by her decision to dismiss 1 300 of the soldiers who had taken part in the protest.

She had consulted President Jacob Zuma on this matter, and he had agreed with the decision to dismiss the soldiers.

"He did not hesitate to indicate his views - immediate dismissal," Sisulu said.

"What we are dealing with here are acts of criminality... I had no option but to take the decision I took."

The dismissed soldiers were not the type of people needed in the defence force. It was not a decision she was prepared to rescind.

"I have discussed this decision with the President, and am not able to rescind it," she said.

Referring to "provisional" dismissal letters sent to the 1 300 soldiers, she said these required a response by Friday. To date, 400 soldiers had responded. If no response was received, the soldier's service would be considered terminated.

The letter called on the soldiers to show reason why they should not be dismissed.

Earlier, Sisulu said the soldiers had, among other things, failed to obey lawful orders not to take part in the illegal protest, undermined national security, and were guilty of act of "outright criminality" on the day.