SEOUL (Kyodo) -- South Korean President Yoon Suk Yeol on Tuesday attended a Constitutional Court hearing for the first time as it considers whether to approve impeachment over his Dec. 3 martial law declaration.

The hearing was the third in the impeachment case at the court, which began earlier this month after the National Assembly passed an impeachment motion on Dec. 14 against Yoon over his brief imposition of martial law, suspending him from all duties.

The court justices are reviewing evidence related to the martial law declaration, with opposition lawmakers arguing that Yoon declared it without meeting the constitutional requirements for imposing the decree.

The president has been held at the Seoul Detention Center since last Wednesday for a separate criminal investigation into allegations that he incited an insurrection by issuing the decree.

Yoon, who was formally arrested Sunday, has refused to be questioned by the Corruption Investigation Office for High-ranking Officials, the agency leading the probe into the insurrection accusation.

In its briefing held earlier Tuesday, the anti-corruption body said it could not prevent Yoon from attending the court hearing as it is his right to do so, Yonhap News Agency reported.

Yoon's defense team has argued that he declared martial law to protect South Korea from opposition parties he described as "anti-state forces" and to safeguard the nation's freedom and constitutional order.