South Korean officials say Somali pirates have released four commercial seamen they had held for 19 months, after the payment of a ransom.

A South Korean foreign ministry official said Saturday the ministry had assisted in ransom talks between the ship's owner and the pirates, but declined to say how much had been paid for their release. The men are now on board a South Korean navy ship.

The sailors were among the crew of the tanker MT Gemini, who were captured on April 30, 2011, while traveling from Kenya to Malaysia.

Seven months later, the pirates freed the vessel, but broke an agreement to release all of the crew, keeping the four Koreans captive, while releasing the 21 non-Korean sailors.

The pirates released most of the crew after the tanker's Singaporean owners paid a ransom reportedly totaling $6 million.

The waters off Somalia are notorious for pirate attacks, but the presence of an international navy task forces has seen such incidents fall sharply this year.