President Yoon Suk Yeol on Thursday rejected calls for his resignation, asserting that his declaration of martial law on Dec. 3 was both an inevitable and legitimate decision made by the head of state, marking another unexpected development that has clearly dismissed the ruling party's "orderly retreat" scenario.

Yoon said in the 29-minute address, televised at around 9:40 a.m., that he pledged to withstand his ordeals until the end, demonstrating his will to respond legally to impeachment proceedings and investigations.

"No matter whether it is an impeachment or an investigation that's ahead of me, I will boldly confront them," he said, reversing his Dec. 7 promise to delegate his power to the ruling party and government.

The address shifted momentum toward impeachment, with the ruling party's Chair Han Dong-hoon and his loyalists announcing their support for Yoon's impeachment on Saturday. Amid escalating internal conflict between factions within the party, Han criticized Yoon, stating that his address "highlighted the president's inability to continue his presidency," urging his party's lawmakers to vote in favor of the impeachment motion.

In a fourth national address in the past two weeks, the beleaguered president said his declaration of martial law was based on "a highly political judgment by the president" to protect the nation and normalize the government.

The president's declaration of martial law is a sovereign act, not subject to judicial review, similar to actions such as presidential pardons and foreign diplomacy, he said.

Any view that his emergency measure was an act of insurrection poses "a serious threat to our Constitution and legal system, as pointed out by many constitutional scholars and lawyers," he added, without elaborating as to who these experts were.

The martial law Yoon declared on Dec. 3, he contended, was intended to serve as a warning to opposition parties, whom he described as "monstrous," "a group of criminals" and an "unconstitutional force," and to inform the people of "anti-state" activities by the opposition parties.

Insisting that a "two-hour martial law" cannot be accused of being an act of insurrection, Yoon said that fewer than 300 troops were dispatched to the National Assembly for "the security of the people" there, and that he ordered them to withdraw as soon as the National Assembly voted to lift martial law.

"If I had wanted to paralyze the functions of the National Assembly, I would have declared a state of emergency on a weekend, not on a weekday," he added. "I would have taken measures to cut off power and water to the National Assembly building and restrict broadcast transmission. But none of that happened."

Following Yoon's address, National Assembly Speaker Rep. Woo Won-shik said in a statement Thursday he was "devastated" and that the president's assertion should not be tolerated.

"(Yoon's claim of) declaring martial law to send a warning to the National Assembly can never be tolerated, because it suggests that democracy and constitutional order can be sabotaged for political goals and people's basic rights can be sacrificed for certain political goals," Woo noted.

Woo proposed an immediate meeting of the ruling People Power Party's Floor Leader Rep. Kweon Seong-dong and his counterpart from the main opposition Democratic Party of Korea, Rep. Park Chan-dae, to "steer clear of instability in the country."

In his address, Yoon repeatedly accused the opposition parties of "abusing power" in that they had brought forward a series of "unconstitutional measures" that made it too difficult for him to sit by and watch.

Yoon also contended that his use of executive power was within the constitutional framework.

"The current state of national paralysis, caused by social unrest and the collapse of administrative and judicial functions, has been deemed a sufficient justification for the declaration of martial law," he said.

In the meantime, Yoon censured the opposition parties for taking sides with North Korea, unilaterally moving to cut budget items he said were essential for the economic growth of the country and wielding their legislative power to block changes in law that would allow for the punishment of spying activities by foreign nationals.

Yoon also said that the opposition parties are rushing to impeach him and pushing for an early presidential election as the conviction of the main opposition party's leader Rep. Lee Jae-myung looms.

Lee is facing multiple trials for separate offenses, any of which could end up disqualifying him from running for president.

The president's impeachment could allow Lee to run for president at an earlier date than the currently scheduled March 2027.

In response, Lee on Thursday told Archbishop Peter Chung Soon-taick, a South Korean prelate of the Catholic Church, that Yoon's speech was "feeding bipolarization" in society, as he was quoted as saying by Democratic Party spokesperson Rep. Han Min-soo.

Four-term lawmaker Rep. Kim Min-seok of the Democratic Party also said Yoon's claim of imposing martial law that was meant to fail indicates that the president is an "extremely delusional" figure.

Moreover, Yoon in his speech disclosed he had ordered then-Defense Minister Kim Yong-hyun to look into the vulnerability of the National Election Commission on the occasion of the martial law imposition.

He said election authorities had refused to comply with the Yoon administration's request to inspect the internal system last year in the wake of North Korean hacks, despite revelations from the National Intelligence Service of security vulnerabilities. The NEC has cited immunity from outside investigation under the Constitution.

As Yoon's remarks hinted at the possibility of election fraud during his term, the NEC countered Yoon's speculation, saying such logic "denies the voting system that led to his victory" in the 2022 presidential election, in a statement Thursday.

Yoon, who previously vowed to entrust power in the prime minister and the ruling party, on Thursday signed 21 bills into law as well as 21 presidential decrees that earlier gained Cabinet approval, according to the Ministry of Government Legislation.