Seoul, South Korea - Two vehicles belonging to South Korean investigators probing impeached President Yoon Suk Yeol arrived outside his official residence early Wednesday as they prepared to execute a new arrest warrant, Yonhap News TV reported.

It came as thousands of the embattled leader's die-hard supporters massed outside the presidential residence in the capital Seoul to protect Yoon, AFP reporters saw.

Yoon's short-lived December 3 imposition of martial law plunged the country into its worst political crisis in decades, after he directed soldiers to storm parliament in an unsuccessful attempt to stop lawmakers voting down his move.

"Two CIO vehicles have arrived in front of the [presidential] residence," Yonhap News TV reported, referring to the Corruption Investigation Office that is probing Yoon's declaration.

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If the court-ordered warrant is successfully executed, Yoon would become the first sitting president in South Korean history to be arrested.

But a first attempt to arrest Yoon on January 3 failed after a tense hours-long standoff with his presidential guards, who refused to budge when investigators tried to execute their warrant.

A joint team of the CIO and police have since secured a new warrant and massed as many as 1,000 personnel for Wednesday's attempt to detain Yoon, according to local media reports.

They have also threatened to detain any guards who obstruct the sitting leader's arrest.

Personnel who appeared to be guarding the entrance from outsiders were seen walking from the residence towards its entrance gate early Wednesday, AFP reporters saw.

Supporters of Yoon were also heard chanting "illegal warrant!" while waving glow sticks and South Korean and American flags.

Yoon's guards have been seen in recent days installing barbed wire and bus barricades at the residence, turning it into what the opposition called a "fortress".

There was heightened security around his compound in central Seoul, with dozens of police buses and scores of uniformed police lining the street outside, AFP reporters saw.

If arrested, Yoon can be held for up to 48 hours on the existing warrant. Investigators would need to apply for another arrest warrant to keep him in custody.

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Yoon's legal team – who say he remains inside the residence – has decried the warrant as illegal and his chief of staff on Tuesday made an appeal for the arrest efforts to stop.

Chung Jin-suk said his office was "ready to consider all options for investigation or visits" to the sitting leader "at a third location".

In a parallel probe, Yoon's impeachment trial began on Tuesday with a brief hearing after he declined to attend.

Although his failure to attend – which his team has blamed on purported safety concerns – forced a procedural adjournment, the hearings will continue without Yoon, with the next set for Thursday.

Additional hearings are scheduled for January 21, January 23, and February 4.