Thousands of South Korean police officers have stormed a church compound in their hunt for a fugitive billionaire businessman over April's ferry sinking that left more than 300 people dead or missing.
Authorities believe the businessman, Yoo Byung Eun, owns the ship and that his alleged corruption may have contributed to the sinking.
Police and prosecutors have been after Yoo for weeks and are offering a US$500,000 reward for tips about him.
Yoo is a member of a group called the Evangelical Baptist Church, which critics say is a cult.
About 5,000 police officers, accompanied by prosecution investigators, raided the group's compound Wednesday in Ansung, just south of Seoul, officers said on condition of anonymity, citing department policy.
Four church members were detained for allegedly providing shelter for Yoo or helping him flee, police said. Another church member was detained for allegedly trying to obstruct the raid.
It was not clear whether Yoo was at the compound at the time of the raid. Police said they were still trying to find and detain more church members for allegedly aiding Yoo.
About 200 church members rallied against the raid, hanging up a large banner that read, "We'll protect Yoo Byung Eun even if 100,000 church members are all arrested."
Yoo, head of the now-defunct predecessor of the ferry's current operator, Chonghaejin, allegedly still controls the company through a complex web of holding companies in which his children and close associates are large shareholders.
The government has offered a US$100,000 bounty for Yoo's eldest son.
The sinking, one of South Korea's deadliest disasters in decades, has caused an outpouring of national grief, and the country is undergoing national soul searching on public safety.
Nearly two months after the sinking, 292 bodies have been recovered - mostly students from a high school near Seoul - and 12 people are still missing.