The Supreme Prosecutors' Office in Seocho District, Seoul, where a meeting is in progress is seen in this Jan. 26 photo. Prosecutors held a national meeting of chief prosecutors to discuss how to handle President Yoon Suk Yeol's martial law case. Yonhap

Prosecutors indicted detained President Yoon Suk Yeol on Sunday on charges of leading an insurrection with his short-lived imposition of martial law last month.

With the indictment, Yoon, who is also facing an impeachment trial, has become the first sitting president in South Korea's history to be indicted under detention.

Yoon faces allegations of conspiring with former Defense Minister Kim Yong-hyun and others to incite an insurrection on Dec. 3 by declaring an unconstitutional and illegal state of emergency, despite the absence of any signs of war, armed conflict or a comparable national crisis.

He is also alleged to have deployed military forces to parliament in an attempt to prevent lawmakers from voting down the martial law declaration.

Yoon is also accused of planning to arrest and detain key political figures, including National Assembly Speaker Woo Won-shik and heads of rival parties, as well as officials of the election watchdog.

The move comes just one day before Yoon's detention period was set to end, following his detention by the Corruption Investigation Office for High-ranking Officials (CIO) on Jan. 15. Yoon was formally arrested on Jan. 19.

The CIO, which had led the investigation into Yoon, transferred the case to the prosecution last week as the agency does not have a legal mandate to indict a president.

Earlier Sunday, senior prosecutors from across the country gathered to discuss the next steps in Yoon's case without having had an opportunity to directly question him.

Prosecutors had sought to question Yoon themselves if his detention was extended but a Seoul court on Saturday rejected the prosecution's request for the second time to extend his detention period.

By law, a suspect must be released if not indicted within the detention period.

The prosecution team investigating the case said they have reviewed the evidence and based on the comprehensive review, it was determined that indicting the defendant was appropriate.

However, with just two days remaining in Yoon's detention, prosecutors must now prove his guilt in court without the opportunity to question him directly.

"The court's denial to extend the detention period twice is difficult to understand, as it prevented even the most basic supplementary investigations, such as questioning the defendant in person," the prosecution said.

Despite such challenges, prosecutors said they have indicted Yoon solely on the charge of leading an insurrection, citing concerns that he might destroy evidence.

Yoon had also faced allegations of abuse of power, but such charges were dropped, as the law grants a sitting president immunity from indictment for charges other than insurrection or rebellion.

Insurrection is punishable by life imprisonment or death. However, South Korea has not carried out an execution in decades.

Yoon Suk Yeol attends the fourth impeachment trial hearing at the Constitutional Court in Jongno District, Seoul, Jan. 23. Yonhap

During last week's impeachment hearing at the Constitutional Court, Yoon and his legal team argued that he never intended to fully implement martial law. Instead, they claimed it was meant as a warning to the opposition party, which Yoon accused of paralyzing state affairs.

The court has up to 180 days to decide whether to impeach Yoon or reinstate him.

The prosecution team investigating the case said they have reviewed the evidence and based on the comprehensive review, it was determined that indicting the defendant was appropriate.

However, with just two days remaining in Yoon's detention, prosecutors must now prove his guilt in court without the opportunity to question him directly.

"The court's denial to extend the detention period twice is difficult to understand, as it prevented even the most basic supplementary investigations, such as questioning the defendant in person," the prosecution said.

Despite such challenges, prosecutors said they have indicted Yoon solely on the charge of leading an insurrection, citing concerns that he might destroy evidence.

Yoon had also faced allegations of abuse of power, but such charges were dropped, as the law grants a sitting president immunity from indictment for charges other than insurrection or rebellion.

Insurrection is punishable by life imprisonment or death. However, South Korea has not carried out an execution in decades.

During last week's impeachment hearing at the Constitutional Court, Yoon and his legal team argued that he never intended to fully implement martial law. Instead, they claimed it was meant as a warning to the opposition party, which Yoon accused of paralyzing state affairs.

The court has up to 180 days to decide whether to impeach Yoon or reinstate him. (Yonhap)