"All the three sailors were freed safe and sound," Lee said on Facebook.

Seoul had deployed an anti-piracy warship to the area after unidentified pirates boarded the 500-tonne Marine 711 with about 40 Ghanaian and three South Korean sailors on March 26.

The pirates seized the South Koreans -- the captain, engineer and mate on the Marine 711 -- and escaped on a separate speedboat.

The freed sailors will be brought home on the South Korean warship, Lee said.

The South's Yonhap news agency had earlier reported that the pirates had been identified as Nigerians, citing South Korea's military.

It is not known whether a ransom was paid to secure the sailors' release.