Former Defense Minister Kim Yong-hyun speaks during a hearing for President Yoon Suk Yeok's impeachment trial at the Constitutional Court in Seoul's Jongno District, Thursday. Courtesy of Constitutional Court

Former Defense Minister Kim Yong-hyun took significant responsibility for President Yoon Suk Yeol's martial law declaration, Thursday, claiming he recommended the emergency military rule and played a key role in its implementation.

He also claimed at least one Cabinet member voiced support for the plan in a meeting held just before Yoon's martial law declaration. But he didn't say who or how many.

Appearing as a witness in Yoon's impeachment hearing at the Constitutional Court, Kim testified that he wrote a controversial note allegedly calling for the establishment of an emergency legislative body under martial law.

This note, which was given to Finance Minister Choi Sang-mok at the Cabinet meeting, has become key evidence in determining the constitutionality of Yoon's Dec. 3 martial law imposition.

When Yoon's lawyer asked who wrote the note, Kim responded, "I did."

Kim explained that Choi, who arrived late to the Cabinet meeting, did not receive the note directly. Instead, Kim passed it on through a working-level official.

The note directed Choi to cut funding to the National Assembly and reallocate resources to establish an emergency legislative body. This has raised questions about whether Yoon intended to dissolve the Assembly — an act that would be unconstitutional even under martial law.

While the Constitution permits special measures regarding press freedoms, executive authority and the judiciary during martial law, it does not allow restrictions on legislative activities.

Kim said he also drew up another note given to Foreign Minister Cho Tae-yul. Cho said he received one directly from Yoon on the night of the martial rule, but did not keep it and he only remembers a few words including "diplomatic offices abroad."

Kim also testified that he had recommended martial law to the president, arguing that it was a necessary move to curb the majority-holding opposition party's wielding of legislative power.

"The president was deeply concerned by the opposition's disregard for the public's livelihoods, focusing instead on shielding their members and pushing for impeachment and special probe investigations," Kim said.

Kim, a retired Army general and close ally of Yoon, is currently under arrest on charges of treason for his role in the six-hour martial law.

Thursday marked his first public appearance since the martial law declaration and his resignation as defense minister on Dec. 5. He appeared in a dark jacket, rather than a prison uniform, and was not handcuffed.

President Yoon Suk Yeol attends a hearing for his impeachment trial at the Constitutional Court in Seoul's Jongno District, Thursday. Joint Press Corps

Yoon, who was also present at the trial, watched as Kim testified. This was the prosecutor-turned-president's second appearance at his impeachment trial after his attendance at a hearing on Tuesday, making him Korea's first president to speak on his own behalf during an impeachment trial.

During the hearing, Yoon questioned Kim about the martial law decree, which both claimed had been drafted by Kim and reviewed by Yoon.

The proclamations included sweeping restrictions, such as a ban on strikes and rallies inciting social unrest. One clause mandated that all medical professionals, including junior doctors who had been on an anti-government strike for nearly a year, must return to work within 48 hours.

"Do you recall me saying that, despite the decree not being specific enough to align with social norms, it should remain untouched, as the martial law would likely last no more than a day?" the president asked.

In response, Kim said, "I felt that the president was not reviewing it as thoroughly as usual. Normally, he would check the law thoroughly, but he didn't that time."

The president then asked if Kim remembered how the return-to-work clause targeting the doctors was included as a guiding measure, although they had both agreed the clause was unrealistic.

"Now that you mention it, I remember," Kim replied.

The former defense minister also downplayed the extent of Yoon's martial law order, claiming the president "had only ordered a small number of troops to the National Assembly," suggesting a lack of intent to seize control of the legislative body.

According to the Ministry of National Defense, about 1,500 troops were mobilized during martial law, with hundreds deployed to the Assembly and others to offices of the National Election Commission.

Conservatives stage a rally near the Constitutional Court in Seoul, Thursday, demanding President Yoon Suk Yeol's release. Joint Press Corps

Hours before Yoon arrived at the hearing, hundreds of the president's loyal supporters gathered near the courthouse, waving Korean and American flags and demanding his immediate release.

Police deployed more than 3,000 officers and 160 buses to manage the protests, wary of the violent demonstrations by Yoon's supporters that erupted at the Seoul Western District Court on Sunday.

The Constitutional Court is set to hold additional hearings on Feb. 4, 6, 11 and 13.

A ruling on Yoon's impeachment is expected before April 18, when the terms of two of the eight justices expire. However, proceedings may be delayed as Yoon's legal team has requested over 20 witnesses, including Cabinet members and senior presidential officials.