Yoon Suk Yeol, South Korea’s ousted president, already on trial on insurrection charges, was rearrested and sent back to jail early on Thursday after a special prosecutor accused him of additional criminal offenses.

Mr. Yoon was impeached by South Korea’s legislature in December​ and arrested in January after a short-lived attempt to place his country under martial law in 2024. He was the first president in South Korean history to be indicted on criminal charges while in office.

In March, a judge released him from jail, saying that prosecutors had made a procedural error by miscalculating how long they could hold ​him in detention before indicting him in January on insurrection charges. That error rendered his detention — but not his indictment — invalid, the judge said.

Mr. Yoon was formally removed from office in April, when the Constitutional Court endorsed his parliamentary impeachment. But since his release from jail, he had been attending his insurrection trial as a free man.

He was often seen roaming around his neighborhood in southern Seoul, the capital, while several former military generals and police chiefs, including his ​former defense minister, remained in jail on charges of helping him to commit insurrection.