Seoul, Jan 31 (IANS): South Korean Constitutional Court has approved the spy agency chief and top security adviser as witnesses to testify at the impeachment trial of President Yoon Suk Yeol, a court official said on Friday.

The court also approved former Third Deputy NIS Director Baek Jong-wook and Kim Yong-bin, secretary-general of the National Election Commission, as witnesses, Cheon said. Baek and Kim are suspected of involvement in the alleged "election fraud" Yoon has cited as a reason for his martial law decree, Yonhap news agency reported.

Former Interior Minister Lee Sang-min is also among the witnesses approved by the court for the trial.

Since the impeachment trial began on December 27, the court has held six hearings, including the two preparatory hearings. Yoon has attended the last two main trial sessions. The next hearing is scheduled for next Tuesday.

Earlier in the day, Yoon met his senior aides at the Seoul Detention Centre and urged them to carry on their work without being discouraged.

Yoon made the call during his meeting with Chung Jin-suk, his Chief of Staff, National Security Adviser Shin Won-sik and three other senior aides at the centre in Uiwang, south of Seoul.

It marked the first visit by Yoon's aides since the impeached President was formally detained on January 19 over allegations of insurrection and abuse of power related to his short-lived imposition of martial law last month.