The foreign ministry says administrative sanctions are being implemented under the passport law against former Navy special warfare officer Rhee Keun, who left for Ukraine to join its international legion of volunteer fighters.

In a Tuesday briefing, ministry spokesperson Choi Young-sam confirmed Rhee's arrival in Ukraine without authorization from the Seoul government.

Choi said passport-related sanctions are underway following consultations with the justice ministry and other agencies. He added that criminal charges for violating the passport law will be pursued later.

Such sanctions can include a government order for Rhee to turn in his passport, invalidation of the passport if he fails to do so, and refusing to issue him a new one.

The Navy SEAL-turned-YouTuber earlier announced his departure for Ukraine to help defend it against Russian invaders. The government imposed a travel ban on all areas of Ukraine on February 13, rendering unauthorized travel to the country a criminal act subject to sanctions and penalties.