South Korean prosecutors raided the offices of state sea traffic controllers, media reports said Sunday, as part of a widening probe into a ferry disaster that left 300 dead or missing.
The move is the latest in an investigation whose scope is broadening as officials scurry to assuage mounting public anger over the April 16 tragedy and the subsequent rescue efforts.
Earlier Sunday, Prime Minister Chung Hong-Won fell on his sword, the most high-profile resignation so far, after admitting he had not been able to prevent the accident or deal adequately with its aftermath.
Prosecutors are already holding all 15 surviving crew members who were responsible for sailing the vessel. They face charges ranging from criminal negligence to abandoning passengers.
On Sunday, prosecutors raided the office of the state-run Vessel Traffic Services (VTS) centre in the southern island of Jeju, Yonhap news agency and other media reported. The VTS is to shipping what air traffic controllers are to aircraft.
Citing prosecutors working on the case, the reports added the VTS centre on the island of Jindo -- the closest bit of land to the wreck -- was also being probed.
The 6,825-tonne ferry was communicating with the two centres -- primarily with Jindo -- for about 30 minutes as it rapidly keeled over and sank, trapping around 300 people inside.
The bodies of 187 of the dead have been recovered, while teams of divers battling decompression sickness and powerful swells are still searching for a further 155.
Investigators have seized records of the VTS radio communication with the Sewol and surveillance video footage from both centres, Yonhap said.
A transcript of the communication between the ferry and the Jindo centre released earlier revealed panic and indecision among crew and sea traffic controllers in the crucial final moments, with neither able to make the call to evacuate passengers.
Businesses connected to ferry operator Chonghaejin Marine Company have also been raided over accusations of corruption, and travel bans are in place for eight current and former executives of the Korea Register of Shipping -- the body responsible for issuing marine safety certificates.