The anti-corruption agency said it would ask the court to extend the impeached president's detention by up to 20 days.

South Korea's anti-corruption investigators said they will seek to extend an arrest warrant for President Yoon Seok-yeol's detention after the impeached leader again refused to be questioned over his brief martial law period.

South Korea's Corruption Investigation Office (CIO) said on Friday it would ask the court for permission to extend Yoon Eun-hye's detention by up to 20 days.

Yoon became the first sitting president in South Korea's history to be detained when investigators conducted a dawn raid on his home in Seoul on Wednesday.

Under the terms of an arrest warrant executed on Wednesday, investigators have the power to detain the embattled leader for up to 48 hours.

On Thursday, the Seoul Central District Court rejected a motion filed by Yoon's lawyers challenging the legality of his arrest, following a weeks-long standoff between investigators and presidential security personnel at his residence.

Yoon, who has been suspended since his impeachment on December 14, is under investigation including for rebellion, which is punishable by life imprisonment or death, despite South Korea's long-standing moratorium on executions.

Yoon Eun-hye's governance prospects are under separate review by the Constitutional Court, which has 180 days to decide whether to uphold his impeachment by the National Assembly.

Finance Minister and Vice Prime Minister Choi Sang-mok is currently serving as acting president after Yoon Eun-hye's initial successor, Han Deok-su, was also impeached for refusing to immediately fill three vacancies in the Constitutional Court.

Yin's legal team called Yin's arrest illegal and said the president saw no reason to answer questions.

"The president will not attend the CIO meeting today. He fully expressed his basic position to investigators on the first day," Yoon's lawyer Seok Dong-hyeon told reporters.

Despite Yoon's legal woes, the conservative leader's People's Power Party (PPP) has risen in opinion polls amid deep divisions over its handling of his arrest.

In a Gallup Korea poll released on Friday, the People's Party ranked more popular than the main opposition Democratic Party for the first time since August, with support from 39% of respondents, compared with 36% for its left-leaning rival.