South Korean President Yoon Suk Yeol on Saturday apologised for his attempt to impose martial law this week but did not resign, defying intense pressure to step down even from some in his ruling party and only hours ahead of a planned impeachment vote.

Yoon said he would not seek to avoid legal and political responsibility for his decision to declare martial law for the first time in South Korea since 1980. He said the decision was born of desperation.

The speech was the embattled leader’s first public appearance since he rescinded the martial law order early on Wednesday, just six hours after it was declared and after parliament defied military and police cordons to vote against the decree.

“I am very sorry and would like to sincerely apologise to the people who were shocked,” Yoon said in a televised address to the nation, during which he bowed.

“I leave it up to my party to take steps to stabilise the political situation in the future, including the issue of my term in office,” he said.

Han Dong-hoon, leader of Yoon's People Power Party (PPP), said after the address that the president was no longer in a position to carry out public duty and his resignation was now unavoidable.

On Friday Han said Yoon was a danger to the country and needed to be removed from power, increasing the pressure on Yoon to quit even though PPP members later reaffirmed a formal opposition to his impeachment.

Han was scheduled to meet Prime Minister Han Duck-soo on Saturday, local Yonhap News reported. Under the constitution if Yoon resigns or is impeached then the prime minister, who was appointed by Yoon, becomes South Korea's interim president.

Lawmakers will vote on the main opposition Democratic Party's motion to impeach Yoon later on Saturday.

Yoon shocked the nation late on Tuesday when he gave the military sweeping emergency powers in order to root out what he called “anti-state forces” and overcome obstructionist political opponents.

Some PPP members urged Yoon to resign before the vote, saying they did not want a repeat of the 2016 impeachment of then-President Park Geun-hye, who left office following months of candlelit protests over an influence-peddling scandal. Her downfall triggered the implosion of the party and a victory by liberals in presidential and general elections.

In scenes reminiscent of those protests, thousands of demonstrators holding candles assembled outside parliament on Friday night demanding Yoon’s impeachment. More demonstrations are expected on Saturday ahead of the vote.

Prosecutors, the police and the Corruption Investigation Office for High-ranking Officials have all launched probes into Yoon and senior officials involved in the martial law decree, seeking to pursue charges of insurrection and abuse of power, among others.

The officials face potential charges of insurrection, abuse of authority and obstructing other people from exercising their rights. If convicted, the crime of leading an insurrection is punishable by death or life imprisonment, with or without prison labour.