South Korea's Yonhap News Agency reports that prosecutors sent a second summons to President Yoon Suk-yeol on Monday over his short-lived declaration of martial law.

The deadline for his appearance for questioning is unknown. Yoon rejected the prosecutors' first request to appear for questioning.

Separately, the joint investigation team into the martial law turmoil -- consisting of officials from police and other investigative organizations -- said also on Monday that it has asked Yoon's presence for questioning on suspicion of insurrection and abuse of power.

The joint team explained that the presidential security service refused to accept the request and replied they are not responsible for handling the matter. The team says it has sent the summons by mail.

Yonhap reports that the team is demanding Yoon appear at 10 a.m. on Wednesday.

Meanwhile, the Constitutional Court said on Monday that it will hold its first preparatory hearing on December 27 to begin Yoon's impeachment trial.

Three positions are currently vacant in the nine-justice court. The ruling and opposition camps of the National Assembly are working on the appointment of three new justices.

Sources in the Constitutional Court say it is possible to proceed with hearings using the current six justices. The sources say the court puts top priority on the impeachment trial.

Yonhap says the chief justice for Yoon's trial, decided by a draw, is a person who was appointed by the president last year as a justice of the Constitutional Court.