Seoul, South Korea - South Korea's suspended President Yoon Suk Yeol will not attend the first hearing of his impeachment trial next week because of safety concerns, his lawyer said on Sunday.

Yoon has been holed up in the presidential residence and protected by an elite guard force since being suspended and impeached last month, following a short-lived declaration of martial law that plunged the country into political chaos.

He has refused to meet prosecutors and investigators and his presidential guard unit thwarted an attempt to arrest him following a tense, hours-long standoff earlier this month.

The Constitutional Court has scheduled five trial dates spanning January 14 to February 4, which will proceed in Yoon's absence if he does not attend.

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"Concerns about safety and potential incidents have arisen. Therefore, the President will not be able to attend the trial on January 14," lawyer Yoon Kab-keun said in a statement sent to AFP. "The President is willing to appear at any time once safety issues are resolved."

The court will decide whether to uphold Yoon's impeachment or restore him to office.

Separately, investigators seeking to question Yoon on insurrection charges linked to his ill-fated martial law declaration are preparing another arrest attempt. His lawyers have repeatedly said an initial seven-day warrant and the new one they secured this week were both "unlawful."

Investigators have kept secret the length of the new warrant, with local media reports saying it is longer than the previous seven days.

Rival protesters for and against Yoon have gathered almost daily in the South Korean capital since the crisis unfolded.

On Sunday, more demonstrations were planned by rival camps outside Yoon's residence and on the streets of Seoul – either calling for his impeachment to be declared invalid or for him to be detained immediately.

The president's legal team say his guards remain on "high alert."

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Yoon would become the first sitting South Korean president to be arrested if investigators are able to detain him.

If convicted, he faces prison or even the death penalty.

A team of Corruption Investigation Office (CIO) officials and police are planning for the next attempt, which they said could be their last.

The CIO said anyone obstructing their attempt could be detained themselves and police reportedly held a meeting of top commanders on Friday to plan for the renewed effort.

Former Presidential Security Service (PSS) chief Park Chong-jun – who resigned on Friday and was automatically replaced by a more hardline Yoon loyalist – told reporters there must be no bloodshed in any second arrest attempt.

The ex-chief faced two days of questioning and did not explain his resignation.

"I am cooperating as diligently as possible with the authorities' investigation," he told reporters Saturday.

His replacement, acting PSS chief Kim Seong-hun, refused to turn up to a third summons on Saturday claiming he had to protect Yoon, opening him up to possible arrest.

Lee Jin-ha, head of the service's security and safety division, was questioned on Saturday.

The National Office of Investigation, a police unit, sent a note to high-ranking police officials in Seoul requesting they prepare to mobilize 1,000 investigators for the fresh attempt, the Yonhap news agency reported.

As the crisis goes on, Yoon's ruling party has seen a bump in approval ratings.

A Gallup survey published Friday showed the People Power Party's approval rating had risen to 34% from 24% three weeks ago.