Unlock the Editor’s Digest for free

Roula Khalaf, Editor of the FT, selects her favourite stories in this weekly newsletter.

South Korea’s opposition parties moved swiftly on Wednesday to impeach President Yoon Suk Yeol, hours after his failed attempt to impose martial law triggered the country’s worst constitutional crisis in decades.

About 190 lawmakers from six opposition parties submitted an impeachment motion, intending to discuss the bill in parliament on Thursday before a vote on Friday or Saturday.

“[Yoon] is someone who can press the button to start war or declare martial law again. He is the one who can put South Korea in biggest jeopardy now,” said Cho Kuk, leader of one of the opposition parties, who urged the country’s legal authorities to arrest Yoon immediately for investigation over treason.

“We should immediately suspend his presidential duties by impeaching him.”

The move to try to oust Yoon heralds further political turmoil in the country of 52mn, Asia’s fourth-largest economy and a key US ally.

It came after the conservative president declared martial law in an unscheduled national broadcast late on Tuesday, saying he needed to purge South Korea of “anti-state forces” and “normalise the country”.

Yoon backed down hours later, lifting the order after it was unanimously rejected by the opposition-controlled legislature. Troops sent to surround the parliament building were withdrawn.

South Korea’s main opposition, the Democratic party, said Yoon’s declaration of martial law “was a grave violation of the constitution”.

“This amounts to a clear act of treason and is a perfect reason to impeach him,” it said in a statement.

“[Yoon] is likely to make another attempt as his first attempt at a martial decree failed,” Lee Jae-myung, the party leader, told a rally in the parliamentary compound. “But we face a bigger risk where he can provoke North Korea and run the risk of an armed clash with North Korea by destabilising the divided border.”

Yoon’s bid to impose martial law — the first in the country since democracy was restored in the 1980s — came after months of tensions with his rivals in parliament.

Following the night of upheaval, South Korea’s financial authorities vowed to prop up markets with “unlimited” liquidity. The Bank of Korea said after an emergency meeting on Wednesday that it was “keeping all options open until the markets stabilise”.

The won, which weakened sharply against the dollar following Yoon’s declaration of martial law, recovered.

The benchmark Kospi index fell nearly 2 per cent. Shares of Samsung Electronics, the country’s biggest company, fell 1.1 per cent.

Any attempt to impeach Yoon would require a two-thirds vote in favour by the 300-member National Assembly. Opposition parties have a total of 192 seats, so a bill could pass with the support of more than eight members of Yoon’s own party.

In the event of a vote for impeachment, Yoon would be suspended immediately from his presidential duties until a final ruling by South Korea’s constitutional court.

A new election must be held within 60 days of a president being removed from office or resigning. The prime minister would take over in an acting capacity.

If lawmakers do not vote for impeachment, there may be more demonstrations, said Choi Jin-bong, a professor of journalism and broadcasting at Sungkonghoe University. “Public protests will likely swell, forcing them to vote for impeachment again,” he said.

Yoon’s abandonment of his attempt to impose martial law was welcomed by the US, South Korea’s most important ally.

Secretary of state Antony Blinken said the US had “watched closely developments over the last 24 hours”.

“We welcome President Yoon’s statement that he would rescind the order declaring emergency martial law,” Blinken said in a statement. “We continue to expect political disagreements to be resolved peacefully and in accordance with the rule of law.”

Earlier, Yoon’s own conservative People Power party called for the president to sack his defence minister, Kim Yong-hyun, who it believes suggested declaring martial law. Party leaders are discussing if Yoon should leave the party, according to state-run Yonhap News.

The Korean Confederation of Trade Unions, the country’s leading umbrella labour group, called for an indefinite strike until Yoon stepped down.