South Korea’s President Yoon Suk-yeol has accepted the resignation of the country’s Defence Minister Kim Yong-hyun and nominated the country’s ambassador to Saudi Arabia, Choi Byung-hyuk, as the new defence minister.

The president’s office confirmed the nomination of Choi, a former army general, as the new defence minister on Thursday, South Korea’s Yonhap news agency reports.

Yonhap said that Kim had proposed to President Yoon that he declare martial law on Tuesday night, a move that was quickly cut short after South Korea’s parliament voted for Yoon to reverse his decision.

Yoon’s nomination of a new defence minister is his first official act since revoking the declaration of martial law in the early hours of Wednesday morning. The reversal sent hundreds of South Korean troops, who had briefly stormed into the National Assembly compound in Seoul, back to their barracks.

Amid public outrage at the attempt to impose martial law and condemnation of Yoon by opposition parties, South Korea’s parliament introduced a motion early on Thursday to impeach the president.

South Korean police also announced on Thursday they were investigating Yoon for “insurrection” – a crime that transcends presidential immunity and can carry the death penalty – after the opposition filed a complaint against him and other key figures involved.

Woo Jong-soo, head of the National Investigation Headquarters of the National Police Agency, told lawmakers that “the case has been assigned,” footage showed.

The crisis in South Korea has unfolded as a mutual defence treaty between North Korea and Russia comes into force.

The Comprehensive Strategic Partnership Treaty, which was signed in June between Russian President Vladimir Putin and North Korean leader Kim Jong Un, came into force on Wednesday, North Korean state media said on Thursday.

The agreement includes a mutual defence pact for immediate military assistance if either Russia or North Korea faces armed aggression.

Chung Jin-suk, Yoon’s chief of staff, said Choi was a fitting choice for the role of new defence minister as he was a retired four-star army general who had served as deputy commander of the South Korea-United States Combined Forces Command from 2019 to 2020.

He described Choi as being a defence minister who would “fulfil the military’s core responsibilities, including maintaining a firm readiness posture based on the robust South Korea-US alliance”, Yonhap reports.