South Korean prosecutors have detained a former aide to President Park Geun-hye, the second person to be held in an influence peddling scandal that has rocked the country's presidency.
Prosecutors have said they are looking into allegations that the former senior adviser, An Chong-bum, and Choi Soon-sil, a long-time friend of the president, forced South Korean conglomerates to donate funds to non-profit foundations using their connections with the president.
On Wednesday, Park replaced her prime minister and finance minister, a reshuffle denounced by political opponents as a bid to divert attention from a crisis that has pushed her approval rating to an all-time low.
Members of opposition parties have called for prosecutors to investigate Park, which would be a first for a sitting South Korean president.
Her nominee to be prime minister, Kim Byong-joon, said on Thursday he believes the president could theoretically be subject to a probe.
Despite numerous scandals over the years, no South Korean president has ever resigned or been successfully impeached.
If Park resigned, an election would be held in 60 days, with the winner serving five years, making for a high-stakes race for which neither of the main parties has prepared.
Prosecutors on Wednesday asked a court for a warrant to arrest Choi, Park's friend at the centre of the scandal, and are seeking to charge her with abuse of power and attempted fraud, court and prosecution officials said. Choi was placed under temporary emergency detention late on Monday.
The Seoul Central Court granted the warrant to arrest Choi late on Thursday, a court official said.
A formal arrest warrant allows her to be held for up to 20 days.
Choi, who has been a friend of Park's for decades but held no formal government role, is alleged to have used her proximity to the president to meddle in state affairs, and her lawyer has said he expects prosecutors to look into whether she inappropriately received classified documents.