Park's arrest warrant is valid for 20 days since execution and the prosecutors have to file formal charges against Park by mid-April before the period expires.

The prosecutors are also likely to seek to conclude their investigation into the scandal as soon as possible to reduce its impact on the May 9 presidential election, sources said.

Park is suspected of having colluded with her close friend Choi Soon-sil to force dozens of local conglomerates to donate a total of 77.4 billion won (US$70 million) to two dubious nonprofit foundations allegedly controlled by Choi.

The prosecution has charged only Samsung's de facto leader, Lee Jae-yong, among business moguls who are suspected of having provided funds to the organizations for business and policy favors.

Lee was arrested for giving or promising some 43.4 billion won to Choi, and in effect to Park, in return for the government's support for the group's merger of two affiliates, which helped tighten his control of the nation's largest business group.

The state prosecutors have been expanding their probe into other conglomerates, including SK, Lotte and CJ groups.

SK Group Chairman Chey Tae-won was grilled by prosecutors two weeks ago. The conglomerate donated a total of 11.1 billion won to the foundations. The prosecution is looking into whether it was in return for a presidential pardon for Chey, who was then serving a prison term for embezzlement and other charges.

The prosecutors are also stepping up their investigation into Park's former senior secretary for civil affairs, Woo Byung-woo, on suspicions that he aided and abetted Choi in meddling in state affairs and disrupted a special presidential inspector's investigation into the scandal.

Last Friday they attempted to raid the presidential office as part of a probe into Woo, but were denied entry by presidential officials who cited security reasons.

Woo also allegedly used his influence to block a prosecution probe into failed rescue efforts during the 2014 sinking of ferry Sewol, which killed 304 people. He is also suspected of having interfered with appointments and inspections of government officials. (Yonhap)