A joint military-police task force has summoned a civilian suspect as part of its investigation of North Korea’s claims that South Korean drones infiltrated its airspace.

The National Office of Investigation at the National Police Agency issued a media statement on Friday, saying it has summoned a civilian for questioning related to the case.

The team added that it cannot disclose the identity of the individual or any other details.

Last week, North Korea accused South Korea of sending drones into the North and said it downed one of them near the border city of Gaesong after the vessel violated the regime’s airspace.

Kim Yo-jong, the sister of North Korean leader Kim Jong-un, separately called on Seoul to provide a detailed explanation for the alleged drone incursions, saying it doesn’t matter whether the drones were operated by the military or civilians.