About 100 sub-contractors have occupied DSME's main dock in the south coast city of Geoje since last month demanding a 30% pay increase, causing delays to deliveries of new vessels.

In recent negotiations, strikers said they lowered their demands to a gradual increase of 15%, while DSME is holding firm at its offer of a 4.5% rise.

"Illegal actions should be resolved swiftly and normalised...for everyone's good," Yoon told reporters in Seoul.

Companies contracted to DSME and the strikers continued talks for more than 12 hours on Wednesday but failed to reach an agreement, as damage compensation emerged as a key sticking point, according to the Korea Metal Workers' Union, which represents the strikers.

The contracted companies had seemed positive about dropping lawsuits seeking damages from the strike but they changed their stance, said the union. DSME, which participated in previous negotiations, did not attend the Wednesday talks, the union added.

A DSME spokesperson declined to comment on details of the negotiations.

South Korea's third-biggest shipbuilder has said the dispute cost it more than $400 million by mid-July.

The construction of eight vessels at five docks at the shipyard is being hampered, with their delivery dates pushed back by two to five weeks as of Wednesday, the DSME spokesperson said.

(Reporting by Byungwook Kim; Editing by Lincoln Feast.)

By Byungwook Kim