South Korean police raided the office of President Yoon Suk Yeol on Wednesday, a lawmaker said, as part of an investigation into his declaration of martial law last week, which plunged the country into a political crisis.

At a parliamentary hearing, Jung Chung-rae, a legislator from the main opposition Democratic Party, said that “the police are conducting a raid on the presidential office.” The police and Mr. Yoon’s office were not immediately available to comment. Mr. Jung is also chairman of the parliamentary committee that deals with judicial matters.

The authorities have barred Mr. Yoon from leaving the country, as prosecutors and the police try to determine whether he and his supporters in the military and the government committed insurrection when they ordered soldiers to enter the National Assembly.

Mr. Yoon is the first sitting president of South Korea to face a criminal investigation, and he now faces the possibility of being arrested while in office. The opposition has accused Mr. Yoon ​of committing insurrection when he sent the troops to the Assembly to block lawmakers from voting against military rule.

Large protests erupted following the imposition of martial law, with people calling for Mr. Yoon’s ouster and impeachment. Tens of thousands of demonstrators gathered outside the National Assembly on Saturday as Mr. Yoon survived an impeachment motion after his party decided to not participate in the vote.

But the widespread anger over Mr. Yoon’s declaration of martial law is yet to subside, and his future is uncertain. His own party has said he is “excluded” from running state affairs. And while it saved Mr. Yoon from impeachment, it has said the plan is to give him an “orderly exit.”

This is a developing story.