The impeached President of South Korea, Yoon Suk Yeol, was released from detention on Saturday under technical and legal grounds but remains under investigation over his declaration of martial law.

A court cancelled 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 court release of the President after the Prosecutor-General instructed the prosecution team to "actively present its arguments before the trial court instead." 

The South Korean President is facing a Constitutional Court ruling on whether to uphold his impeachment and officially remove him from office, with a decision expected soon.

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.

The opposition criticized the court decision to release Yoon, Democratic Party leader Lee Jae-myung saying that they would "fight until the insurrection is over," during a rally.

The former president, who was detained in January over his attempt to impose Martial Law on December 3, was seen smiling while walking out of the detention center before bowing to a small group of his supporters in front of the center.