By Ju-min Park and Christine Kim
SEOUL (Reuters) - South Korean special prosecutor officials withdrew from the presidential Blue House on Friday after it blocked them from searching offices there, in the latest twist in a corruption scandal that has gripped the country for months.
Park was impeached by parliament on Dec. 9 on suspicion of colluding with a long-time friend, Choi Soon-sil, to pressure big business to donate to two foundations set up to back the president's policy initiatives.
Park is also accused of allowing Choi to exert inappropriate influence over state affairs. Both of them have denied wrongdoing.
The special prosecution office has not explained why it needs to search the Blue House, saying only that it would be done in connection with its investigation.
A prosecution team trying to carry out a search on Friday was blocked at a gate into the compound, the office said.
The prosecution said later it had asked acting President Hwang Kyo-ahn for cooperation in getting access to search the presidential offices.
"We arrived at the conclusion we cannot force our search if the subject refuses," Lee Kyu-chul, the spokesman for the special prosecutor, told a media briefing.
Lee said he believed the search could go ahead if the acting president gave his approval.
The Blue House expressed regret and called the attempt to search the presidential office unconstitutional as the president can not be charged with a crime while in office.
"It is a deep regret that their excessive investigation with a warrant naming the president as a suspect violates the constitution," the office said in a statement, referring to the prosecutor's warrant to raid the office.
The law states that as long as Park remains president, she cannot be charged with any criminal offense except insurrection or treason.
The Blue House said earlier the offices could not be searched for security reasons and it would instead provide documents as requested by prosecutors.
Park was stripped of her powers after parliament voted to impeach her, but she remains in the Blue House compound.
Her prime minister, Hwang, has been acting president since then, while she waits for the Constitutional court to either uphold or reject the parliamentary vote.
Television broadcaster YTN had said the prosecutor's office wanted to search the offices of the Blue House chief of staff, as well as offices used by Park's bodyguard detail.
No raid has ever been successfully carried out on the Blue House.
Lee, the spokesman for the special prosecutor's team, said investigators would question the president in person, regardless of the outcome of their effort to search her office.
Prosecutors were also searching the offices of the Korea Fair Trade Commission and the Financial Services Commission in their investigation of Samsung Group, whose leader, Jay Y. Lee, has been named a suspect in the scandal.
He has denied wrongdoing.
A Korea Fair Trade Commission spokesman confirmed that investigators were conducting a raid but did not comment on details. A spokeswoman for the FSC said prosecutors were making copies of documents and searching offices.
The FSC spokeswoman said the raid was linked to prosecutors' suspicion that the Samsung Group had provided bribes to Park and Choi for favours regarding its businesses.
If Park's impeachment is upheld by the Constitutional Court, she will become the first democratically elected leader in South Korea to be removed from office.
(Additional reporting by Se Young Lee; Editing by Nick Macfie, Robert Birsel)