The Corruption Investigation Office for High-ranking Officials (CIO) confirmed the Seoul Western District Court approved an arrest warrant requested by investigators examining Yoon s short-lived imposition of martial law, Reuters reported.

Yoon is facing investigation on allegations that he was the leader of an insurrection, one of the few criminal charges from which a South Korean president does not have immunity. The arrest warrant for an incumbent president is unprecedented, and deepens the political crisis that has engulfed South Korea, Asia s fourth-largest economy and a key U.S. ally.

Prime Minister Han Duck-soo, who took over from Yoon as acting president, has also been impeached by parliament, which is dominated by the opposition.

Finance Minister Choi Sang-mok, who took over as acting president after Han s impeachment, has been dealing with Sunday s crash of Jeju Air flight 7C2216, which killed 179 people in the deadliest air disaster on South Korean soil.

The current arrest warrant is viable until Jan. 6, and once it is exercised, Yoon is expected to be held at the Seoul Detention Center, Yonhap news agency said, citing the CIO.

Yoon Kab-keun, a lawyer for the impeached president, said the arrest warrant was illegal and invalid because the CIO did not have the authority under South Korean law to request a warrant.

The district court issued the warrant due to the likelihood that Yoon will not respond to summons without a justifiable reason, and there being a substantial reason to suspect Yoon of a crime, Yonhap said. The court declined to comment.

It was unclear when or how the arrest warrant for Yoon will be carried out. South Korea s presidential security service said in a statement on Tuesday that it will treat the arrest warrant according to due process.