Four sailors abducted by Somali pirates 19 months ago were released yesterday, South Korea's foreign ministry said.

The MT Gemini, a tanker operated by Singapore-based Glory Ship Management, was hijacked by the pirates on April 30, 2011 while heading to Malaysia from Kenya.

The pirates freed the vessel seven months later along with the 21 non-Korean crew, but kept the four Koreans captive, breaching an earlier agreement.

Officials added that the sailors, now on a South Korean navy ship, were undergoing health checks.