Oh Dong-woon, chief prosecutor of the Corruption Investigation Office for High-Ranking Officials, told a parliamentary hearing on Monday he has instructed investigators to seek a travel ban.
The office is one of several law enforcement bodies, including public prosecutors and police, investigating the circumstances around Mr Yoon’s declaration of martial law.
Mr Yoon’s martial law decree last week, which brought armed special forces troops into the streets of Seoul, is plunging South Korea into huge political turmoil.
On Sunday, he avoided an opposition-led bid to impeach him, with most ruling party lawmakers boycotting a floor vote.
But the opposition parties vowed to submit a new impeachment motion against him this week.
On Monday, a senior National Police Agency officer told reporters in a background briefing that police are considering banning Mr Yoon from leaving the country as they investigate him on charges of rebellion.
The officer said police can also detain the president if conditions are met.
The main opposition Democratic Party called Mr Yoon’s martial law imposition “unconstitutional, illegal rebellion or a coup.” It has filed complaints with police against at least nine people, including Mr Yoon and the former defence minister, over the alleged rebellion.
While the president mostly has immunity from prosecution while in office, that does not extend to allegations of rebellion or treason.
South Korean prosecutors on Sunday detained former defence minister Kim Yong Hyun, who allegedly recommended the martial law declaration. He became the first person detained over the martial law case.
The Defence Ministry said it has separately suspended three top military commanders over their alleged involvement in imposing martial law.
They were among those facing the opposition-raised rebellion allegations.
During a briefing on Monday, the Defense Ministry said Mr Yoon maintained control of the military, a power the constitution explicitly reserves for the president.
On Saturday, Mr Yoon issued an apology over the martial law decree, saying he would not shirk legal or political responsibility for the declaration. He said he would leave it to his party to chart a course through the country’s political turmoil, “including matters related to my term in office”.
Since taking office in 2022 for a single five-year term, Mr Yoon has struggled to push his agenda through an opposition-controlled parliament and grappled with low approval ratings amid scandals involving himself and his wife.
In his martial law announcement on Tuesday night, Mr Yoon called parliament a “den of criminals” bogging down state affairs and vowed to eliminate “shameless North Korea followers and anti-state forces”.
