Thousands of supporters of arrested former President Park Geun-hye were expected to gather in South Korea's capital on Saturday to call for her release.
Seoul police planned to deploy more than 10,000 officers to monitor the rally near City Hall amid concerns of clashes. Opponents and supporters of Park have divided the streets of Seoul in recent months with passionate rallies.
Park was jailed Friday over allegations that she colluded with a confidante to extort money from businesses, take bribes and allow the friend to unlawfully interfere with state affairs.
Dozens of her supporters rallied outside the detention center Friday, some of them crying and bowing toward the facility while vowing to "protect" her.
Three people died amid violent clashes between Park's supporters and police on March 10 after the Constitutional Court decided to remove her from office.
Park's presidential powers were suspended after lawmakers impeached her in December, following weeks of massive demonstrations by millions of people calling for her ouster.