A South Korean retired military official said on Friday that the resignation of the country's defence minister, Kim Yong-hyun, implies that the ministry is taking full responsibility for the short-lived imposition of martial law earlier this week.

President Yoon Suk-yeol declared martial law on Tuesday evening, before agreeing to lift it just several hours later after the National Assembly voted against the move.

Speaking to RTHK, Lieutenant General Chun In-bum, who retired in 2016, said the army did not have advance knowledge of Yoon's decision.

"The army were not aware why martial law was being declared and what their mission was in detail. They were told just a couple of hours before their mission was to occupy certain government buildings to include the National Assembly. Many of them even did not know where they were going until they arrived there," he said.

Chun added that the army's reputation is unharmed, but morale has been affected.

"The reputation of the army is intact because the soldiers involved knew that something was wrong and did not pursue the given mission very proactively, thereby allowing the democratic system to work," he said.

"I hope that the Korean people understand that the army had nothing to do with it. They were under orders from their commander-in-chief, who was the president of Korea. They probably thought that he was giving them a bona fide task."

Chun said the country has to come up with arrangements to maintain law and order and avoid similar events from happening again.

But he stressed that South Korea requires martial law to be an available option, so as to counter threats from North Korea.