Pirates who seized a Comoros-flagged Aris 13 oil tanker have released the ship without conditions in the first seizure of such a vessel since 2012.
Regional forces are also mobilising in a bid to free the ship.
"The master confirmed that armed men were on board his ship and they were demanding a ransom for the ship's release".
The Aris 13 sent a distress call on Monday, turned off its tracking system and altered course for the Somali port town of Alula, said John Steed of the aid group Oceans Beyond Piracy.
The development came after negotiations between local elders and the gang that had seized the vessel on Monday. An unnamed Somali official said the firefight erupted after authorities tried to intercept a boat carrying supplies to the pirates. "They made (the pirates) an offer they couldn't refuse and the pirates have left".
Lim urged the Federal Government of Somalia, as well as its regional authorities in Puntland to take immediate action toward the safe release of the eight Sri Lankan seafarers.
"We don't have facts, but we heard perhaps they moved away from Alula because they received hostile reception from their locals and they felt under pressure to move", Abdirazak Mohamed Dirir, Puntland counterpiracy director, told VOA. "They are being held under guard in a single compartment in the ship".
Yesterday, EU navy forces said the pirates have demanded undisclosed ransom from the owners of the vessel to release it from custody.
Illegal fishing has always been used by Somali pirates as an excuse for attacks and Steed has in the past warned that the presence of foreign vessels emptying Somali waters could reverse the gains against piracy.
But the pirates said they agreed to forego a ransom after learning that Somali businessmen had hired the ship, which was taking oil from Djibouti to the Somali capital of Mogadishu. At the peak of the piracy epidemic in January 2011, 736 hostages and 32 boats were held.
A United Nations report seen by the AP in November said Somali pirates retain the capacity and intent to resume the attacks and lately have shifted to targeting smaller foreign fishing boats.
Though anti-piracy measures ended attacks on commercial vessels, fishing boats have continued to face attacks.