Prosecutors launched an investigation into around 10 police and military officials Thursday for their alleged involvement in President Yoon Suk Yeol's brief declaration of martial law earlier this month.

Prosecutors seized mobile phones belonging to Woo Jong-soo, chief of the National Office of Investigation, as well as several other police and military officials, as part of their probe into the office, the Seoul Yeongdeungpo Police Station and the Ministry of Defense's investigative unit.

Judicial sources said prosecutors were also questioning Yoon Seung-young and Jeon Chang-hoon, two key officials of the NOI, as witnesses.

Yoon is under investigation on insurrection charges related to his short-lived martial law decree on Dec. 3 and has been suspended from duty pending a Constitutional Court trial following his impeachment by the National Assembly.

The NOI under the Korean National Police Agency is suspected of sending a team of homicide detectives to join the operation of the so-called "arrest team" tasked with apprehending key political figures at the request of the Defense Counterintelligence Command after the martial law was imposed.

The NOI previously noted that it had provided a list of around 10 detectives after receiving the request at 11:32 p.m. that day.

However, the office did not confirm whether officers were actually dispatched to the National Assembly, although prosecutors believe they were.

Prosecutors are expected to analyze the call logs from the seized phones to determine whether the counterintelligence command contacted police personnel stationed at the parliament.

The Defense Ministry's investigative unit is suspected of sending 10 military police investigators in response to a request from the Martial Law Command's joint investigative unit following the martial law declaration.

Woo expressed "extreme regret" over the seizure of his phone, emphasizing that the police would continue to fulfill their responsibilities in the martial law investigation under the joint task force framework.

The joint investigation team comprises police, the Corruption Investigation Office for High-ranking Officials and the Ministry of Defense's investigative unit.

The NOI has been vying with prosecutors for investigative control of the martial law attempt, arguing that only police have jurisdiction over investigations into insurrection cases. (Yonhap)