South Korean President Yoon Suk Yeol on Thursday lashed out at his political opponents as "anti-state forces", said North Korea has hacked the country's elections, and defended his short-lived martial law order as a legal move to protect democracy.

Yoon said the opposition was "dancing the sword dance of madness" by trying to drag a democratically elected president from power, nine days after his aborted attempt to grant sweeping powers to the military.

"I will fight to the end," he said in a lengthy address broadcast on television. "Whether they impeach me or investigate me, I will face it all squarely."

His comments, the first since he apologised on Saturday and promised to leave his fate in the hands of his political allies, came as the leader of his ruling People Power Party (PPP) said if Yoon did not resign he must be impeached.

"I propose we adopt a vote for impeachment as party policy ... His address was akin to confessing to insurrection," PPP leader Han Dong-hoon told a meeting of party members in the latest sign that Yoon was losing his grip on power.

Yoon faces a second impeachment vote in parliament expected on Saturday, a week after the first one failed because most of the ruling party boycotted the proceedings.

If it succeeds, the case would go to the Constitutional Court to determine the legitimacy of Yoon's presidency, a process that could leave Asia's fourth-largest economy and key U.S. ally in political limbo for up to six months.

The president is also under criminal investigation for alleged insurrection over the Dec. 3 martial law declaration, which he rescinded hours later, sparking the biggest political crisis in South Korea in decades.

In comments that echoed his justification for declaring emergency rule in the first place, Yoon said the "criminal groups" that have paralysed state affairs and disrupted the rule of law must be stopped at all costs from taking over government.

He was referring to the opposition Democratic Party which has blocked some of his proposals and raised allegations of government wrongdoing, but he gave no evidence of criminal activity.

A member of the Democratic Party leadership, Kim Min-seok, said Yoon's address was a "display of extreme delusion" and called on members of the president's ruling party to vote to impeach him.

NORTH KOREAN HACK

Yoon also spoke at length about an alleged hack by communist-ruled North Korea into the National Election Commission (NEC) last year, again without citing evidence.

He said the attack was detected by intelligence agents but the commission, an independent agency, refused to cooperate fully in an investigation and inspection of its system.

The hack cast doubt on the integrity of the April 2024 election - which his party lost in a landslide - and led him to declare martial law, he added.

The NEC said it had consulted with the National Intelligence Service last year to address "security vulnerabilities" but manipulating elections was "effectively impossible."

Troops entered the election commission's computer server room after Yoon's martial law declaration, officials said and closed-circuit TV footage showed, but it was not clear if they removed any equipment.

Yoon's party suffered a crushing defeat in the April election, allowing the Democratic Party overwhelming control of the single-chamber assembly.

Even so, the opposition still needs eight PPP members to vote with them for the president to be impeached.

Yoon defended his decision to declare martial law as a "symbolic" move intended to expose an opposition plot to "completely destroy the country" and collapse the alliance with the United States.