SEOUL (Reuters) - A U.S. bribery case against two relatives has cast a pall over former United Nations chief Ban Ki-moon’s planned return this week to South Korea, where he is expected to launch a bid to run for president.

Ban, 72, has not declared his candidacy but has had a team of people laying the groundwork in Seoul for a possible presidential campaign ahead of his planned arrival in South Korea on Thursday.

The former foreign minister consistently polls as a top candidate as South Korea braces for the possibility of an early election following parliament’s December impeachment of President Park Geun-hye in an influence-peddling scandal.

If a Constitutional Court upholds the impeachment, Park would become South Korea’s first democratically elected leader to leave office in disgrace, triggering an election two months later.

Lee Do-woon, Ban’s spokesman, was quick to distance Ban from an indictment filed against Ban’s younger brother and his nephew in a Manhattan federal court. It accuses Ban’s relatives of a scheme to bribe a Middle Eastern official for an attempted $800 million sale of a building complex in Vietnam.

“Ban was greatly surprised by the news, which he learned from the media. He knows nothing about it,” said Lee, who also said Ban would address various concerns upon his arrival in South Korea.

Ban would take at least two weeks to decide whether he will run for president instead of taking to the campaign trail immediately, as many analysts and observers had expected, Lee told a media briefing.

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Lee also asked supporters to refrain from greeting Ban on his arrival at Incheon airport. Ban would be driven to his residence in Sadang in southern Seoul instead of taking public transport, as South Korean media had reported.

Controversy around the building deal linked to Ban’s relatives has been previously reported in South Korean media.

In September, a Seoul district court ordered Ban’s nephew to pay civil damages of about $590,000 to builder Keangnam Enterprises. The court said the nephew had fraudulently led Keangnam to believe that the Qatar Investment Authority was close to buying the Vietnam skyscraper.

Ban said during a 2015 visit to South Korea that he had nothing to do with his nephew’s business and that he was “embarrassed” by the situation.

The two relatives could not be reached for comment and Ban also was not immediately available for comment.

“MUST BE CONVINCING”

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Though Ban has not declared an intention to run for president he has said he would devote himself to the country after his U.N. tenure ended.

“What he needs to do is draw a line and say he has nothing to do with (the alleged improprieties), and he needs to be convincing in his explanation. Otherwise people will start doubting him,” said Kim Sang-jin, professor of political science at Konkuk University.

“If he mishandles this people will start thinking that he is too weak or isn’t as clean as they thought he was,” Kim said.

Ban plans to travel through South Korea to speak to the public until late January, his spokesman said.

He will visit the National Cemetery on Friday and then a community center, Lee said, and will then go to Chungju in North Chungcheong province to visit his mother and other family members there on Saturday.

He will also visit a welfare center for the elderly and homeless before returning to Seoul on Sunday.

Ban does not belong to any political party and has been out of the country for most of the past decade. However, a party, funds and political machinery to support him could come together quickly if and when he announces he will run for president on what is widely expected to be a conservative platform.

He had until recently been tipped to run as a member of Park’s Saenuri party.

However, being a Saenuri candidate looks far less attractive now because of the influence-peddling scandal and he has been seen as likely to join a new breakaway group from the conservative bloc.

If Ban joins the new group he is likely to have competition.

Yoo Seong-min, a prominent lawmaker from the new party announced on Wednesday he would announce a formal bid for the presidency on Jan. 25.

Ban’s spokesman declined to comment on which party Ban might join.