South Korea's President Yoon Suk-yeol has again refused to appear for questioning, despite a request by a joint team of investigators on Monday.

The investigation team notified Yoon that he would be questioned at 10 a.m., but he refused. The president was arrested on Sunday on suspicion of orchestrating an insurrection by declaring martial law last month.

Sources related to the Corruption Investigation Office for High-ranking Officials told reporters that investigators could visit the detention center. But the sources also said the most likely option would be to forcibly bring the president to the anti-corruption agency building to interrogate him there.

Yoon appeared for questioning last Wednesday after he was detained by the investigation team, but has refused to comply with requests for further questioning.

The team plans to detain the president until early February.

The Justice Ministry said Yoon was transferred to a solitary cell of around 12 square meters after his arrest. It also said the president agreed to allow police to take his headshot.