The team of special counsel Cho Eun-suk seeks a 30-year prison term for former President Yoon Suk Yeol over drone dispatch to Pyongyang at the Seoul Central District Court in Seoul, April 24. Yonhap

The defense ministry is investigating how the drones sent into North Korea ahead of former President Yoon Suk Yeol's failed martial law attempt were brought into service, amid allegations of irregularities in the process, an official said Friday.

The ministry has launched a joint internal probe with the state arms procurement agency into how drones were sent into Pyongyang in October 2024, weeks before the former president's Dec. 3 martial law attempt, a ministry official said.

The drone incursion issue has been at the center of allegations surrounding the martial law case amid suspicion that they were sent across the border to incite the North's provocations in a bid to use it as a pretext for the martial law imposition.

"A joint internal audit is currently under way with the Defense Acquisition Program Administration (DAPA) at the request of the National Assembly," the official told reporters.