According to a lawyer on Thursday, South Korea's impeached President Yoon Suk Yeol vowed to "fight until the end" as he faces an arrest attempt over his brief martial law declaration last month.

The timing and method of the arrest remain unclear, and there are concerns about potential interference from his presidential security service. Tensions escalated on Thursday as police clashed with Yoon's supporters, who blocked the road to his home in protest, resulting in the removal of several demonstrators.

Yoon said in the letter late on Wednesday to the hundreds of supporters gathering near his official house that he was watching their "hard work" on Youtube and vowed to "fight until the end to protect this country with you."

'Yoon committing an insurrection'

The opposition Democratic Party, which has majority control of parliament and spearheaded Yoon's impeachment on December 14, claimed the letter demonstrated Yoon's delusions and his determination to accomplish his "insurrection".

"As if trying to stage an insurrection wasn't enough, he is now inciting his supporters to an extreme clash," party spokesperson Jo Seoung-lae said in a statement.

On December 3, Yoon stunned the country with a late-night announcement that he was declaring martial law to break the political gridlock and ferret out "anti-state forces".

Within hours, however, 190 MPs disregarded the military and police cordons and voted against Yoon's directive. Yoon revoked his first ruling almost six hours later.

In a historic moment, a South Korean court approved on Tuesday the arrest of President Yoon Suk Yeol, who had been impeached by parliament and temporarily suspended from office, the first time in South Korea's history that a sitting president has faced an arrest warrant. 

The Corruption Investigation Office for High-ranking Officials (CIO) confirmed that the Seoul Western District Court authorized the arrest warrant, which was sought by investigators probing Yoon's brief declaration of martial law.

Yoon is under investigation for allegedly leading an insurrection, one of the few criminal charges that can be brought against a South Korean president, as they do not enjoy immunity from such accusations. Additionally, his impeachment trial is ongoing at the Constitutional Court.

A CIO official told reporters at a briefing on Tuesday that the current arrest warrant for Yoon is valid until January 6, adding that Yoon could be held at a police station or the Seoul detention center.

The lawyer warned that police personnel would risk arrest by "the presidential security service or any citizens" if they attempted to detain Yoon on behalf of the CIO, claiming that their jurisdiction is restricted to crowd management and keeping public order.

Separately, the Constitutional Court is hearing Yoon's impeachment trial. The court will have its second hearing on Friday. Yoon has been suspended from his presidential responsibilities, and Finance Minister Choi Sang-mok has taken over as acting president until the trial's result.

If the court supports the impeachment and Yoon is ousted from office, a new presidential election will take place within 60 days.