South Korea’s Acting President Han Duck-Soo Resigns

South Korea’s acting president, Prime Minister Han Duck-soo, stepped down on Thursday, a sign that he plans to run to inhabit the role permanently in the June 3 presidential election.

Mr. Han has indicated for weeks that he was mulling over whether to run for the June election, which was called after the impeachment and ouster of former President Yoon Suk Yeol, who had appointed Mr. Han as the No. 2 official in his administration.

Mr. Han’s resignation came shortly after the country’s Supreme Court made a ruling that could jeopardize the presidential bid of Lee Jae-myung, the presidential candidate of the country’s majority Democratic Party who polls show is the current front-runner to win the election.

That ruling threatens to add uncertainty to an election that South Koreans hope will bring an end to months of political turmoil in the country since Mr. Yoon declared martial law late last year, a short-lived episode that led to him being removed from office. Mr. Han replaced Mr. Yoon for a while but then was impeached himself, before being restored as acting president by the Constitutional Court.

“I have decided to step down to do what I can do and what I should to help overcome the crisis our nation faces,” Mr. Han said in a statement on Thursday.

Mr. Han stopped short of saying he would run for president. But his statement on Thursday was regarded by South Korean news media and political circles as a de facto declaration of presidential ambition. Mr. Han was expected to call a news conference later this week to make his presidential bid official, local news media reported.

Earlier Thursday, the country’s Supreme Court overturned a lower-court ruling that had acquitted Mr. Lee of election-law violations, returning the case for retrial. The Supreme Court said in its ruling that it considered Mr. Lee guilty, but the case against Mr. Lee will not be over until the lower court rules again and the Supreme Court reviews that ruling as well.

Mr. Lee’s ability to run for president depends on when the lower court will rule again and what type of penalty he will get should the court find him guilty this time. By law, Mr. Lee will be barred from running in elections for five years if he receives a penalty heftier than a 1 million won ($700) fine.

It was not clear when the lower court will start deliberating the case again.

The Supreme Court’s ruling on Thursday cast a cloud over Mr. Lee’s presidential ambition by enabling his political enemies to raise questions about his qualifications to lead the nation.

Mr. Lee was elected his party’s presidential candidate with overwhelming support on Sunday. He won nearly 90 percent of the votes cast during his party’s primary race.

Mr. Lee has been the front-runner by a large margin in public opinion surveys in recent weeks that asked South Koreans who they favored as president.

Some politicians affiliated with the People Power Party have been urging Mr. Han to run for president. The party, the country’s second-largest, will select its candidate on Saturday, and that person and Mr. Han may have to negotiate to decide who should represent the party in the election. Currently, Mr. Han does not belong to a party.

Following Mr. Han’s resignation, Finance Minister Choi Sang-mok, the next in line in the government hierarchy, takes over as acting president.