Pirates in the port town confirmed they were expecting the ship.
According to media reports, the vessel was carrying fuel oil from Djibouti to Somalian capital Mogadishu yesterday when it was approached by two skiffs.
All available EU Naval Force assets are continuing to monitor the situation.
Former Somali pirates arrested by sailors aboard European Union warships in the Seychelles stand behind a locked gate at the prison where they are serving a 25-year sentence in Garowe, Puntland state in northeastern Somalia, on December 14, 2016.
The Aris 13 was forced to dock near the town of Alula, in northeastern Somalia's semi-autonomous region of Puntland.
Australian government records from 2014 show the ship in Monday's incident was owned by Flair Shipping Trading FZE in the United Arab Emirates and linked to UAE-based ship management firm Aurora Ship Management FZE.
A Somali pirate who said he was in touch with the armed men onboard the tanker said the amount of ransom to demand had not yet been decided.
Pirate hijacks are usually carried out for ransom, but no ransom request has yet been made.
A volatile buildup of weapons and resentment along the northern Somali coast culminated in the hijack of an oil freighter this week, the first such seizure by Somali pirates since 2012, experts and locals say. He said the Aris 13 has a crew of eight Sri Lankan sailors.
"So this is not a pirate attack, it's angry fishermen trying to protect their area so that they can fish", said Harare Ahmed Mohamed Matan, a fisherman in Puntland, in a phone interview.
Aircraft from regional naval force EU Navfor were reported to have been called to track the ship's progress. Argyrios Karagiannis, the managing director of Flair Shipping, declined to comment.
That year, Ocean's Beyond Piracy estimated the global cost of piracy was about $7 billion. The vessel was hijacked by suspected Somali pirates Monday.
Salad Nur, an elder from Putland, Somalia, told the Associated Press that local fishermen and former pirates were behind the hijack.
Local fishermen, the report noted, were getting a fraction of the fish while illegal foreign trawlers were making away with thousands of tonnes of fish. They do not normally kill hostages unless they come under attack.
The Aris 13 drifted toward the Somali coast near the far eastern tip of Africa, possibly in an attempt to save time, according to John Steed, an expert in maritime crime at Oceans Beyond Piracy, a nonprofit group based in Colorado.