Police reinforcements will be deployed in key areas, while subway stations and at least one school will close for safety reasons as South Korea's Constitutional Court decides whether to reinstate or remove impeached President Yoon Suk Yeol.

Yoon's political future remains uncertain after his brief martial law decree on December 3 resulted in impeachment and separate insurrection charges.  

A ruling could come as early as this week, with large crowds expected from both his supporters and opponents following recent protests that drew tens of thousands.

Lee Ho-young, Acting Commissioner General of the National Police Agency, told reporters, "We are setting up plans considering the worst-case scenarios," adding that police officers are authorized to use pepper spray or batons if violence erupts, as seen during Yoon supporters' rampage on a court building in January.

Additionally, the Seoul Metropolitan Office of Education advised six schools near the court to take safety measures, including closing on ruling day, according to official Kim Eun-mi.

One school decided to close for the day, Kim said.

'Prosecution took too long to indict him'

On Saturday, Yoon was released from detention under technical and legal grounds but remains under investigation over his declaration of martial law.

A court canceled Yoon's arrest warrant on procedural grounds, a verdict that was called "unjust" by prosecutors who were investigating the impeached President after they waived the right to appeal the court's decision.

Prosecutors did not appeal the president's court release after the prosecutor general instructed the prosecution team to "actively present its arguments before the trial court instead."

Yoon's lawyers filed to cancel his arrest last month, saying that his detention was unlawful because the prosecution took too long to indict him, noting that his "release signifies the restoration of the rule of law," his legal team stated.