Embattled South Korean President Yoon Suk Yeol has defended his shock decision to declare martial law last week, saying he did it to protect the country's democracy.

In a surprise televised address on Thursday, he said the attempt was a legal decision to "prevent the collapse" of democracy and counter the opposition's "parliamentary dictatorship".

And despite growing calls for him to resign or be impeached, Yoon has suggested that he would not step down.

"I will stand firm whether I'm impeached or investigated," he said. "I will fight to the end".

The president and his allies are currently facing investigations on insurrection charges, and a travel ban has been slapped on several of them.

But Yoon has denied that his martial law order was an act of insurrection, claiming that his political rivals were now creating "false incitement" to bring him down.

In his address, his first since his apology on Saturday, he repeated many of the same arguments that he used on the night he declared martial law: that the opposition was dangerous, and that by seizing control, he had been trying to protect the public and defend democracy.

However, Yoon added that he would not avoid his "legal and political responsibilities".

Last weekend, an attempt by opposition lawmakers to impeach the president failed, after members of his own ruling party boycotted the vote - but opposition members are set to hold another impeachment vote this weekend and have vowed to hold one every Saturday until Yoon is removed from office.

Yoon's party had been hoping to convince the President to leave office early, rather than force him out.

Minutes before Yoon spoke, his party leader, Han Dong Hoon, appeared on television saying it had become clear he was not going to step aside. Han then urged members of the party to vote to remove him from office this Saturday.

If South Korea's parliament passes an impeachment bill, a trial would be held by a constitutional court. Two-thirds of that court would have to sustain the majority for Yoon to be removed permanently from office.

Yoon has been a lame-duck president since the opposition won a landslide in the country's general election in April this year - his government has not been able to pass the laws it wanted and has been reduced instead to vetoing bills the opposition has proposed.