South Korea’s leadership crisis deepened on Sunday when prosecutors named President Yoon Suk Yeol as the subject of a criminal investigation into last week’s attempt to declare martial law and its former defense minister was arrested.

Yoon survived an impeachment vote in the opposition-run parliament late Saturday that was triggered by his short-lived attempt to impose martial law on Tuesday, but the leader of his own party said the president would be effectively barred from his duties before he finally resign.

That proposal, which appeared to receive the tacit approval of Yoon’s appointed prime minister on Sunday, was condemned by opposition lawmakers who said it was another unconstitutional power grab to delegate authority without resignation or impeachment.

Thousands of people gathered outside parliament in Seoul on Sunday, demanding Yoon’s impeachment and arrest and the dissolution of his ruling party.

Yoon’s declaration of martial law on Tuesday plunged Asia’s fourth-largest economy and a key U.S. military ally into its biggest political crisis in decades and threatened to destroy South Korea’s reputation as a democratic success story.

Yoon’s People Power Party chairman Han Dong-hoon said at a news conference alongside the prime minister on Sunday that Yoon would not interfere in foreign and other state affairs before his early resignation.

But National Assembly Speaker Woo Won-shik said it was unconstitutional to delegate the president’s authority to the prime minister and the ruling party without impeachment. Woo suggested a meeting of rival parties to discuss ways to immediately suspend Yoon’s power as president.

The main opposition Democratic Party called for the immediate suspension of Yoon’s presidency and the withdrawal of his powers to control the military. The DP called for the arrest of Yoon and related military officials involved in the martial law fiasco.

Yoon shocked the nation on Tuesday night when he gave the military sweeping emergency powers to stamp out “anti-state forces” and obstructive political opponents. He revoked the order six hours later after Parliament defied military and police barricades and voted unanimously against the decree.

Yonhap News Agency reported that prosecutors had “indicted” Yoon, a process in South Korea that involves formally naming subjects under investigation. Prosecutors could not immediately be reached for comment on the report.

Three opposition minority parties filed a complaint with prosecutors against Yoon, former defense minister Kim Yong-hyun and martial law commander Park An-su, accusing them of insurrection. The crime of leading an insurrection is punishable by the death penalty or life imprisonment, with or without prison labor. Kim, who resigned on Wednesday after Yoon lifted martial law, was seen as a central figure in the debacle.

According to a senior military official and the impeachment files, he had suggested martial law to the president. The prosecutor’s special investigation team arrested Kim on Sunday and confiscated his cellphone, it said in a brief statement to reporters.

Before the arrest, investigators questioned Kim, who voluntarily appeared at the Seoul Central District Prosecutor’s Office at around 1:30 a.m. on Sunday (16:30 GMT on Saturday), Yonhap News Agency reported.

National police searched Kim’s office on Sunday as part of an investigation into treason allegations against Yoon and senior ministers, Yonhap said. Opposition lawmakers claim Yoon mobilized military forces to block a vote by lawmakers seeking to annul what they said was an unconstitutional martial law resolution.

Hours before Saturday’s impeachment vote, Yoon addressed the nation in a televised speech to apologize for his martial law decree and said he would put his fate in the hands of his party. Han said the remarks were effectively a promise to leave office early, adding that the ruling party would consult the prime minister to manage state affairs.

Prime Minister Han Duck-soo said on Sunday the Cabinet would do its best to “maintain trust in our allies,” referring to the United States and Japan. The ruling party gave few details about its plan to prevent Yoon’s impeachment but force him into power, and the proposal added more confusion to the crisis over presidential authority. In an effort to reassure the public, several military leaders, including the acting defense secretary, have said they would reject any order to impose another round of martial law.

The Defense Ministry on Sunday did not respond to repeated questions from foreign media about who is now the commander in chief of South Korea’s military, which is among the largest in the world and has joint commands with the United States.

“I think (military commanders) are very disappointed, some of them feel they have been betrayed. It will take a lot of work to regain the trust of the military,” said Chun In-bum, a retired lieutenant general in the South Korean Army region and a former commander of the country’s special forces, who blamed politicians for the chaos.

“I resent the fact that they use the military to do their job, and it was a bad decision to use the military to solve a political problem,” Chun said. Analysts say the leadership crisis threatens to undermine allied efforts to deter North Korea with nuclear weapons.

“North Korea will likely take a wait-and-see approach to these events, but it cannot be ruled out that Pyongyang will seek to exploit divisions in Seoul,” said Leif-Eric Easley, a professor at Ewha University in Seoul.