South Korea's ruling party chief showed support Friday for suspending the constitutional powers of President Yoon Suk Yeol for imposing martial law this week, in a bombshell reversal that makes Yoon's impeachment more likely.

Opposition parties are pushing for a parliamentary vote on Yoon's impeachment on Saturday, calling his short-lived martial law declaration an "unconstitutional, illegal rebellion or coup." But they need support from some members of the president's People Power Party (PPP) to get the two-thirds majority required to pass the impeachment motion. 

The turmoil resulting from Yoon's nighttime martial law decree has frozen South Korean politics and caused worry among neighbours, including fellow democracy Japan, and Seoul's top ally, the United States, as one of the strongest democracies in Asia faces a political crisis that could unseat its leader.

During a party meeting, PPP leader Han Dong-hun stressed the need to suspend Yoon's presidential duties and power swiftly, saying he poses a "significant risk of extreme actions, like reattempting to impose martial law, which could potentially put the Republic of Korea and its citizens in great danger."

Han said he had received intelligence that Yoon had ordered the country's defence counter-intelligence commander to arrest and detain unspecified key politicians based on accusations of "anti-state activities" during the brief period martial law was in force.

"It's my judgment that an immediate suspension of President Yoon Suk Yeol's official duties is necessary to protect the Republic of Korea and its people," he said.

Han on Thursday had said he would work to defeat the impeachment motion even though he criticized Yoon's martial law declaration as "unconstitutional." He said there was a need to "prevent damage to citizens and supporters caused by unprepared chaos."

Thousands of protesters have marched in the streets Seoul since Wednesday, calling for Yoon to resign and be investigated. Thousands of autoworkers and other members of the Korean Metal Workers' Union, one of the country's biggest umbrella labour groups, have started hourly strikes since Thursday to protest Yoon. The union said its members would begin indefinite strikes on Dec. 11 if Yoon was still in office then.

Impeaching Yoon would require support from two-thirds of the National Assembly, or 200 of its 300 members. The opposition parties who jointly brought the impeachment motion have 192 seats. PPP has 108 lawmakers.

Eroded ties between Han, Yoon

Han was previously regarded as a close associate of Yoon as they spent years working together as prosecutors and he served as Yoon's first justice minister. But after Han entered party politics and became PPP leader, their ties soured as they differed over how to handle scandals involving Yoon and his wife.

Han leads a minority faction within the ruling party, and 18 lawmakers in his faction voted with opposition lawmakers to overturn Yoon's martial law decree. Martial law ultimately lasted about six hours, after the quick overrule by the National Assembly forced Yoon's cabinet to lift it before daybreak Wednesday.

Cho Kyoung-tae, a senior ruling party lawmaker who supports Yoon's impeachment, told reporters that each party lawmaker must now decide "whether they want to take the people's side or become collaborators of martial law forces."

If Yoon is impeached, he would be suspended until the Constitutional Court rules on whether to remove him from office or restore his presidential power. Prime Minister Han Duck-soo, the country's No. 2 official, would take over presidential responsibilities.

The main opposition Democratic Party leader Lee Jae-myung said in a separate televised speech Friday that it was crucial to suspend Yoon as "quickly as possible." 

Lee said Yoon's martial law enforcement amounted to "rebellion and also a self-coup." He said Yoon's move caused serious damage to the country's image and paralyzed foreign policy, pointing to criticism coming out of the Biden administration and foreign leaders cancelling their visits to South Korea.

Yoon has made no immediate response to Han's comments. He hasn't made public appearances since he made a televised announcement that his martial law decree had been lifted. But his office said Thursday that Yoon accepted the resignation offer of Defence Minister Kim Yong-hyun, who opposition parties and Han alleged recommended the martial law imposition to the president. 

The prosecution on Thursday placed an overseas travel ban on the former defence minister.

Prosecutor General Shim Woo Jung told reporters Friday that the prosecution plans to investigate rebellion charges against Yoon following complaints filed by the opposition.

While the president mostly enjoys immunity from prosecution while in office, the protection does not extend to allegations of rebellion or treason. It wasn't immediately clear how the prosecution plans to proceed with an investigation into Yoon.

Democratic Party spokesperson Jo Seoung-lae said Friday the party is considering filing a legal complaint against PPP floor leader Choo Kyung-ho, whom they accuse of attempting to facilitate Yoon's martial law enforcement.

Choo, a Yoon loyalist, had asked party lawmakers to convene at the party's headquarters rather than the National Assembly ahead of a crucial vote on Wednesday, which ultimately passed unanimously with 190 votes in favour of lifting the martial law.

The Biden administration, which has worked closely with Yoon's government while strengthening trilateral security co-operation with Japan to counter North Korean threats and regional instability, has expressed deep concern about Yoon's actions.

In a telephone conversation with South Korean Foreign Minister Cho Tae-yul, U.S. Secretary of State Antony J. Blinken welcomed the lifting of martial law following the parliamentary vote and conveyed his confidence in South Korea's democratic resilience, the State Department said.