South Korea will hold a presidential election on May 9 to replace impeached leader Park Geun-hye, who was dismissed last Friday over a corruption scandal, the Yonhap news agency reports.
Prime Minister Hwang Kyo-ahn, who has also been acting president since December, said earlier he would not run for president in the election.
Hwang became acting as president when parliament impeached Park in December. The Constitutional Court upheld Park's impeachment last Friday and dismissed her from office.
Hwang had emerged in opinion polls as a top conservative candidate even though he never declared an intention to run.
The Constitutional Court dismissed Park from office on Friday when it upheld a parliamentary impeachment vote over an influence-peddling scandal that has shaken South Korea's political and business elite.
Park has denied any wrongdoing.
The Samsung Group, South Korea's largest conglomerate, is already embroiled in the scandal and the Yonhap news agency said prosecutors had started investigating two other conglomerates - the Lotte Group and SK Group.
Samsung denies any wrongdoing. A spokesman for the SK Group said it would co-operate with the investigation, while the Lotte Group could not be reached immediately for comment.
Park was summoned to appear for questioning on Tuesday, the prosecutors' office said in a message to media.
Minister of the Interior Hong Yun-sik promised the May 9 vote would be the most clean and transparent ever.
"This election is unprecedented in our history," Hong told a briefing, referring to the short campaign period.
The Park scandal has undermined support for the ruling conservatives, and Hwang's decision would appear to bolster the chances of a prominent liberal, Moon Jae-in, who is leading in opinion polls.
