South Korean prosecutors on Sunday said they have requested court approval to detain the head of the military drone unit as part of a probe into former President Yoon Suk Yeol and drone operations in North Korea.

The special counsel team last week summoned the chief of the Drone Operations Command, Kim Yong-dae, over allegations that Yoon ordered a covert drone operation into the North last year to inflame tension between the neighbors to justify his martial law decree. The impeached Yoon has denied the allegations, Reuters news agency reported.

On Friday, Kim told reporters that the incident was part of a “clandestine military operation” in response to trash balloons from the North and not to provoke the neighbor.

In October, North Korea said the South had sent drones to scatter anti-North Korea leaflets over Pyongyang, and published photos of the remains of a crashed South Korean military drone.

South Korea at the time declined to disclose whether it had sent the drones.

Kim was arrested on Friday without a court warrant, local media reported.

Prosecutors and police are permitted to conduct an “emergency arrest” if they have a strong belief that someone is guilty of a serious crime and that there is a risk that the individual might flee or destroy evidence.

Prosecutors stepped up investigations into the drone operation after indicting the jailed ex-President Yoon on additional charges for his short-lived declaration of martial law in December.