The owners of two ships involved in South Korea's worst oil spill have been charged with breaking pollution laws.
The clean-up operation is continuing in Taean
More than 12,000 tonnes of crude oil spilled into the sea last month after an industrial barge snapped its tow lines and collided with a super tanker.
Chinese firm Hebei Ocean Shipping and Samsung Heavy Industries have now been charged with polluting the ocean.
Three people have committed suicide as part of large-scale protests against officials' handling of the disaster.
Ji Chang-hwan, a fish-seller, drank poison before dousing himself with flammable liquid and setting himself alight at a rally in Taean county on Friday.
He died in hospital the following day.
Prosecutors announced on Monday that Hebei Ocean Shipping, which owns the tanker, and the barge's operator, Samsung Heavy Industries, would be charged.
"We've been searching for and confiscating evidence to find new facts, but it is difficult at this moment to clearly say which side is more responsible and to what extent," prosecutors told Korea's Yonhap news agency.
The spill was the largest in South Korea's history
The three South Korean captains of the barge and its two tugboats, along with two Indian nationals who operated the Hong Kong-registered Hebei Spirit, have been charged with polluting the ocean and professional negligence.
The spill happened when a tug snapped its towing cable, causing the barge it was pulling to drift and collide with the super tanker in Taean county, about 150km (95 miles) south-west of Seoul, in early December.
Tens of thousands of police, troops and volunteers staged a huge clean-up of the shoreline but environmentalists say the damage to the ocean bed could last for years.
The tourism and fishing industries on a scenic stretch of the country's western coastline have been very badly damaged.
The oil slick, the largest in South Korea's history, was about a third of the size of the 1989 Exxon Valdez oil spill in Alaska, considered the costliest on record.
South Korea's previously largest spill happened in 1995, when 5,000 tonnes of oil washed on to the southern coast.