Data on incidents reported to IMO shows that the hijack of the tanker Aris 13, on 13 March, is the first reported hijack of a vessel covered by IMO regulations by Somali pirates since the tanker Smyrni in May 2012. Somali maritime police attempted to intercept a boat that was carrying supplies to the pirates but were fired at by the hijackers.
Families of the crew members had tearfully pleaded for the men to be released unharmed.
The tanker, which was en route from Djibouti to the Somali capital, Mogadishu, was seized on Monday with eight Sri Lankan crew members on board.
The gang said they agreed to forego a ransom after finding out that Somali businessmen had hired the tanker.
The Puntland authorities deployed local forces in the area in an attempt to assist rescue efforts for the hostages on board the vessel, the district commissioner said.
Security official Ahmed Mohamed told the AP news agency that pirates agreed to leave after negotiating with local elders and state officials.
EU Naval Force maritime patrol aircraft is thought to be overlooking the hijacking and has tried to make contact with the ship's master.
Earlier, the hijackers have claimed to be fishermen whose livelihood undermined from foreign fishing ships in Puntland waters amid growing frustration against Puntland government for granting fishing permits to foreign ships.
The Aris 13 on Monday reported being approached by two skiffs, John Steed with the organization Oceans Beyond Piracy said.
The Sri Lankan foreign ministry has confirmed that eight of its nationals are on board the vessel.
Pirates have traditionally been wary of getting caught up with the country's powerful businessmen.
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.
"These are fishermen who are infuriated with the illegal fishing off their coasts".
The Sri Lanka-flagged ship is owned by Armi Shipping SA and is operated by Aurora Ship Management, both based in the United Arab Emirates.
However, some smaller fishing vessels have recently been seized in the area.