South Korea's suspended President Yoon Suk Yeol did not respond on Wednesday to a second summons by anti-corruption authorities who, along with prosecutors, are investigating his short-lived martial law decree issued early this month.

South Korea’s President Yoon Suk Yeol again declined to appear for questioning by investigators over his martial law declaration as the embattled leader seeks to first defend himself at an impeachment trial.

The Constitutional Court will decide whether to remove Yoon sometime in the next six months. If he is removed from office, a snap election will be called.

The lawyers for a former South Korean defence minister under investigation on insurrection charges said on Thursday a short-lived martial law decree imposed earlier this month was to raise alarm on opposition parties' abuse of the democratic process.

Impeached South Korean President Yoon Suk Yeol likely kept the United States in the dark about his plan to declare martial law to avoid interference, the National Assembly speaker said.

A summons for Mr Yoon to appear for questioning over alleged insurrection was delivered to the presidential residence on Tuesday but returned, the agency quoted a joint investigation team as saying. If he responds to the summons, it will be the first time in history that a sitting president appears before prosecutors as a suspect.

South Korea's main opposition party said it will introduce a bill to impeach acting President Han Duck-soo on Thursday (December 26) and hold a vote in parliament on Friday (December 27), in a move that could deepen the country's constitutional crisis triggered by suspended president Yoon Suk Yeol’s short-lived martial law.

South Korean President Yoon Suk Yeol failed to appear before law enforcement authorities for questioning on Wednesday - the second time he has ignored a summons over his attempt to impose martial law.