South Korean law enforcement authorities are pushing to summon impeached President Yoon Suk Yeol for questioning over his short-lived martial law decree, as the Constitutional Court began its first hearing on Yoon's case on Monday to determine whether to remove him from office or reinstate him.

A joint investigation team including police, an anti-corruption agency and the defense ministry plans to send a request to Yoon's office to appear for questioning on Wednesday as they expand an investigation into whether his arrest of ill-conceived power meant a rebellion.

Yoon was impeached by the opposition-controlled National Assembly on Saturday over his Dec. 3 martial law decree. His presidential powers will be suspended until the Constitutional Court decides whether to formally remove him from office or reinstate him. If Yoon is removed, an election to choose his successor must be held within 60 days.

Yoon has justified his imposition of martial law as a necessary act of government against an opposition he described as "anti-state forces" that are swamping their agendas and vowed to "fight to the end" against efforts to impeach him of the position

Hundreds of thousands of protesters have taken to the streets of the country's capital, Seoul, in recent days, calling for Yoon's impeachment and arrest.

LOOK | South Korea's parliament votes to impeach the president:

South Korea's parliament votes to impeach the president by martial law

South Korea's parliament on Saturday voted to impeach President Yoon Suk Yeol over his short-lived martial law decree, a historic rebuke that was cheered by jubilant crowds who described the result as another challenging moment in the resilient journey democratic of the nation.

It is not yet clear whether Yoon will agree to investigators' request for an interview. South Korean prosecutors, who are pushing a separate investigation into the incident, also asked Yoon to appear at a prosecutor's office for questioning on Sunday, but he refused to do so. Repeated calls to a prosecutor's office in Seoul were not answered.

Yoon's office has also resisted an attempt by police to search the compound for evidence.

The request came ahead of the Constitutional Court meeting to discuss the case later on Monday. The court has up to 180 days to rule, but observers say a court decision could come sooner.

In the case of the parliamentary impeachments of former presidents — Roh Moo-hyun in 2004 and Park Geun-hye in 2016 — the court took 63 days and 91 days, respectively, before deciding to reinstate Roh and fire Park.

LOOK | How South Korean Politics Got Out of Control:

Martial Law: How South Korean Politics Got Out of Control | About This

In the last 24 hours, South Korean President Yoon Suk Yeol declared martial law, only for his decision to be unanimously rejected in a parliamentary vote. Andrew Chang explains the uproar the president's statement caused and what it says about the state of South Korean politics. Images supplied by Reuters and Getty Images.

Prime Minister Han Duck-soo, who will act as the country's acting leader while Yoon's powers are suspended, and other government officials have sought to reassure allies and markets after Yoon's surprise paralyzed politics , halted high-level diplomacy and complicated efforts to revive a sagging economy.

Liberal opposition leader Lee Jae-myung, whose Democratic Party has a majority in the National Assembly, urged the Constitutional Court to quickly rule on Yoon's impeachment and proposed a special council to to the political cooperation between the government and the parliament.

Lee, a fiery lawmaker who for years led a political offensive against Yoon's government, is considered the favorite to replace him. He lost the 2022 presidential election to Yoon by a very slim margin.

Kweon Seong-dong, floor leader of Yoon's conservative People's Power Party, separately criticized Lee's proposal, saying it was "not right" for the opposition party to act as the ruling party.

Yoon's impeachment, which was approved in parliament by some of his ruling People's Power Party lawmakers, has created a deep rift within the party between Yoon's loyalists and his opponents. On Monday, PPP chairman Han Dong-hun, a strong critic of Yoon's martial law, announced his resignation.

"If martial law had not been lifted that night, a bloody incident could have erupted that morning between the citizens who would have taken to the streets and our young soldiers," Han told a news conference.

Yoon's imposition of martial law on Dec. 3, the first of its kind in more than four decades, harkens back to an era of authoritarian leaders the country had not seen since the 1980s. Yoon was forced to lift his decree hours later after parliament voted unanimously to overturn it.

Yoon sent hundreds of soldiers and police officers to parliament in an effort to stop the vote, but they withdrew after parliament rejected Yoon's decree. No major violence occurred.

Opposition parties have accused Yoon of rebellion, saying a South Korean president can only declare martial law in times of war or similar emergencies and would not have the right to suspend parliament operations, even in these cases.