A South Korean court granted on Sunday an extension of impeached President Yoon Suk Yeol's detention, saying there was "concern" that Yoon could "destroy evidence" in a criminal probe related to his short-lived declaration of martial law in early December.

Last Wednesday, Yoon became the first sitting South Korean president to be arrested. Investigators probing Yoon for alleged insurrection asked a court in Seoul on Friday to extend his detention after he refused to be questioned.

The Seoul Western District Court said it approved the detention warrant requested by the Corruption Investigation Office for High-ranking Officials (CIO).

The reason for the approval was "concern that the suspect may destroy evidence," the court said in a statement.

Under the new warrant, Yoon can be detained for up to 20 days. He is being held at the Seoul Detention Centre.

So far, Yoon has stonewalled efforts by the CIO to interrogate him, refusing to attend questioning. It was unclear if he will co-operate with investigators during his extended detention.