South Korean opposition MPs will vote to impeach President Yoon Suk-yeol for his botched attempt to impose martial law, and police say they are investigating claims of treason against him and top ministers.
Yoon's declaration of martial law late on Tuesday sought to consolidate power, ban political activity and censor the media, sparking outrage in the streets and concern among South Korea's international allies.
The defence minister, who recommended the move, has resigned.
MPs of the opposition Democratic Party plan to seek a vote in parliament to impeach Yoon on Saturday night.
"The Yoon Suk-yeol regime's declaration of emergency martial law caused great confusion and fear among our people," Democratic Party MP Kim Seung-won told the National Assembly on Thursday.
Yoon's ruling People Power Party is divided over the crisis but said it would oppose impeachment, with the party in turmoil and two years left in Yoon's five-year term.
The Democratic Party needs at least eight of the 108 ruling-party MPs to back the bill for it to pass with a two-thirds majority in the 300-seat parliament.
Fighting for his political future, Yoon accepted the resignation of Defence Minister Kim Yong-hyun on Thursday and nominated his ambassador to Saudi Arabia, Choi Byung-hyuk, as a replacement.
Kim had recommended Yoon declare martial law, according to the interior minister, a senior military official and the opposition's filing to impeach Yoon.
Kim also ordered the deployment of troops to the parliament, Vice-Defence Minister Kim Seon-ho said, adding he was unaware of the martial law order until Yoon declared it.
"I have fundamentally opposed the mobilisation of military forces under martial law and have expressed negative opinions about it," Kim Seon-ho told a parliament hearing on Thursday, apologising and taking responsibility for failing to prevent it.
The chief of investigations for the national police confirmed to a parliamentary hearing that the force was investigating accusations of treason and crimes over the declaration of martial law.
The complaint was filed by an opposition party and activists.
The probe includes Yoon, his interior minister, and the ousted defence minister.
On Wednesday, Secretary of State Antony Blinken told Reuters the United States had not been made aware in advance of Yoon's declaration, while his deputy, Kurt Campbell, said Yoon had badly misjudged it.
The United States has 28,500 troops stationed in South Korea as a legacy of the 1950-1953 Korean War.
Yoon had been embraced by Western leaders as a partner in the US-led effort to unify democracies against growing authoritarianism in China, Russia and elsewhere.
But he caused unease among South Koreans by branding his critics "communist totalitarian and anti-state forces".
In November, he denied wrongdoing in response to accusations of influence-peddling against him and his wife, and he has taken a hard line against labour unions.
The impeachment plan follows a night of chaos after Yoon declared martial law and armed troops attempted to force their way into the National Assembly building in Seoul, only to stand back when parliamentary aides sprayed them with fire extinguishers.
The troops' commander said he had no intention of wielding firearms against the public, and the vice-defence minister said no live ammunition had been provided.
"The people and the aides who protected parliament protected us with their bodies. The people won, and it's now time for us to protect the people," the Democratic Party's Kim said.
Many protesters said they feared a return to the dictatorships and martial law that marked much of South Korea's postwar period.
If the impeachment bill passes, South Korea's Constitutional Court will decide whether to uphold the motion, a process that could take up to 180 days.
If Yoon were to be suspended from exercising power, Prime Minister Han Duck-soo would fill in as leader.
If Yoon resigned or was removed, an election would be held within 60 days.
Yoon, a career prosecutor, won the tightest presidential election in South Korean history in 2022, riding a wave of discontent over economic policy, scandals and gender wars.
But his support ratings have been about 20 per cent for months and the opposition captured nearly two-thirds of parliament seats in an April election.
