The four released on Wednesday were sailors of the MV Prantalay 12 vessel, a Taiwanese flagged fishing vessel seized by Somali pirates on April 18 2010, said the UN Special Representative for Somalia Nicholas Kay.
The ship was used by the pirates as a base before it eventually capsized in July 2011 and the remaining crew members were taken ashore, said Kay.
Six members of the original crew of 24 succumbed to illness and 14 crew members from Myanmar were released to the Puntland Maritime Police authorities and repatriated in May 2011, Kay said in a statement.
"I am grateful to see the longest held hostages released from Somalia, and thank all those involved who made it happen, especially the regional authorities in Galmudug," Kay said. Somali pirates are still holding 26 more hostages, abducted from the FV Naham 3, Kay said.
Also Read
A USD 1 million ransom was paid for the release of the four Thai crew members, said Bile Hussein, a Somali pirate. His claim could not be independently verified.
The majority of hostages held by Somali pirates have been sailors on merchant ships, though European families have also been kidnapped from their yachts while travelling in the dangerous Indian Ocean coastal waters. Four Americans were killed in February 2011 when pirates boarded their ship despite the presence of US warships nearby.