South Korean prosecutors are seeking to formally arrest the former defence minister alleged to have colluded with President Yoon Suk Yeol in imposing martial law last week, as authorities investigate whether their acts amount to rebellion.

Martial law, the first in more than 40 years, lasted only about six hours but has triggered a domestic firestorm and large street protests. Yoon and his associates face criminal investigations and impeachment attempts. The Justice Ministry has banned Yoon and eight others from leaving the country as authorities see them as key suspects in the martial law case. It’s the first time that a sitting president in South Korea has received a travel ban.

The Seoul Central District Court said Tuesday it will review a request from prosecutors for a warrant to arrest former Defence Minister Kim Yong Hyun, who has been accused of recommending martial law to Yoon and sending troops to the National Assembly to block lawmakers from voting on it. Enough lawmakers eventually managed to enter a parliament chamber and unanimously rejected Yoon’s decree, forcing the Cabinet to lift it before daybreak on December 4.

Kim said in a statement Tuesday that he "deeply apologises for causing significant anxiety and inconvenience". He said all responsibility for the imposition of martial law rests solely with him and pleaded for leniency for soldiers deployed to enforce it, saying they were only following his order.

Kim has been detained since Sunday. If an arrest warrant is issued, he would be the first person arrested in the case. Prosecutors would have up to 20 days to investigate Kim and determine whether to indict him. A conviction on the charge of rebellion would carry up to the death penalty.

Prosecutors reportedly accuse Kim of playing a key role in a rebellion and committing abuse of power by staging a riot to disrupt the constitution in collaboration with Yoon and other military and police officers. Prosecutors' offices in Seoul couldn't immediately confirm the reports.

During a parliamentary hearing Tuesday, Kwak Jong-keun, commander of the Army Special Warfare Command whose troops were sent to parliament, testified that he received direct instructions from Kim Yong Hyun to obstruct lawmakers from entering the National Assembly’s main chamber. Kwak said the purpose of Kim’s instructions was to prevent the 300-member parliament from gathering the 150 votes necessary to overturn Yoon’s martial law order.

At the same hearing, senior officer Kim Dae-woo of the military’s counterintelligence agency said his commander, Yeo In-hyung, asked him if an army bunker in Seoul had space to detain politicians and other figures after martial law was imposed. Yeo is considered a close associate of Kim Yong Hyun. Last week, Hong Jang-won, first deputy director of South Korea’s National Intelligence Service, said Yoon ordered him to help Yeo’s command to detain some of his political rivals but he ignored the president’s order.

Kwak and Yeo are among those who face opposition-raised rebellion charges along with Yoon and Kim, and the Defence Ministry suspended them last week.

Opposition parties and many experts say the martial law decree was unconstitutional. They say a president is by law allowed to declare martial law only during “wartime, war-like situations or other comparable national emergency states” and South Korea wasn’t in such a situation. They argue that deploying troops to seal the National Assembly to suspend its political activities amounted to rebellion because the South Korean Constitution doesn’t allow a president to use the military to suspend parliament in any situation.

In his martial law announcement, the conservative Yoon stressed a need to rebuild the country by eliminating “shameless North Korea followers and anti-state forces” in a reference to his liberal rivals who control parliament. Since taking office in 2022, Yoon has been on a near-constant collision course with the main liberal opposition Democratic Party, which has introduced motions seeking to impeach some of his top officials and launched a fierce political offensive against Yoon over a spate of scandals involving him and his wife.

The focus of attention now is how authorities can investigate Yoon and whether they can detain him.

South Korean law gives a president immunity from prosecution while in office, except for allegations of rebellion or treason. This means that Yoon can be questioned and detained by investigative agencies over his martial law decree, but many observers doubt that authorities will forcefully detain him because of the potential for clashes with his presidential security service. They also say the security service won’t likely permit searches of Yoon’s office, citing a law that prohibits searches of sites with state secrets without approval from those in charge of those areas.

In the case of former President Park Geun-hye, who was thrown out of office in 2017 after being impeached by parliament over a corruption scandal, prosecutors failed to search her office and ended up receiving documents outside the compound because presidential officials turned them away. After refusing to meet with prosecutors while in office, Park underwent questioning by them and was arrested after the Constitutional Court approved her impeachment and ruled to dismiss her as president in March 2017.

Yoon avoided impeachment on Saturday after most governing party lawmakers boycotted a floor vote in the National Assembly. The Democratic Party said it would prepare for a new vote on Yoon's impeachment on Saturday. The party on Tuesday submitted motions to impeach Yoon’s police chief and justice minister as well. It pushed to impeach Kim Yong Hyun and the safety minister, but they resigned before parliament took a vote.

If Yoon is impeached, his presidential powers would be suspended until the Constitutional Court decides whether to restore his powers or remove him from office. If it voted for removal, a new presidential election would be required.