Citing an official of the Ministry of Oceans and Fisheries, the broadcaster said the ministry delayed the operations to win favors from Moon in terms of expanding its staff number and affiliated organizations.

The National Election Commission has asked SBS officials about the allegations and the ministry official whose identity was withheld in the report, a commission official said.

The investigation is aimed at determining whether the broadcaster or the official violated election laws by disclosing false information to prevent the election of a particular candidate.

South Korea is to pick a new president next Tuesday, with Moon leading polls by a wide margin. In the latest opinion surveys published Wednesday, the former human rights lawyer beat his closest competitor Ahn Cheol-soo of the center-left People's Party with support of about 40 percent against some 20 percent.

His campaign has lodged a strong complaint with SBS, saying the report is "fake news." The broadcaster deleted the report from the Internet and later issued an apology, claiming it had no intention of affecting the election or slandering a particular candidate.

It also claimed the report was deleted to stop the allegations from spreading, not due to external pressure.

Other presidential contenders, however, demanded the truth.

"This is not time to delete the truth but to reveal it, and apologize before our children," Park Jie-won, chief of the People's Party, said on Facebook, referring to the 250 high school students who died in the sinking. "Don't burn your own soul in the desire for power."

Park also accused Moon's campaign of strong-arming the media.

Meanwhile, the campaign of Hong Joon-pyo of the conservative Liberty Korea Party demanded Moon immediately quit the race if the allegations are true. (Yonhap)