Pirates have hijacked an oil tanker off the coast of Somalia in the first the first such incident involving a large commercial vessel there since 2012, Somali officials and piracy experts said.

The Aris 13, which had been carrying fuel from Djibouti to Mogadishu, reported being approached by two skiffs on Monday, according to the organisation Oceans Beyond Piracy.

Flt Lt Louise Tagg, a UK-based spokeswoman for the EU naval force operation off Somalia, confirmed that an incident involving an oil tanker had occurred and an investigation was under way.

An official based in the Middle East said eight Sri Lankan crew members were on board the vessel. The official, speaking anonymously, said it was unclear why the ship stopped off in northern Somalia, an area known to be used by weapons smugglers and the al-Qaida-linked extremist group al-Shabaab.

The official said no ransom demand had been made.

“The vessel’s captain reported to the company they were approached by two skiffs and that on one of them they could see armed personnel on board,” the official said. “The ship changed course quite soon after that report and is now anchored.”

It was not clear who owned the ship or where it was flagged. Oceans Beyond Piracy said it was owned by the United Arab Emirates and Sri Lankan-flagged, but the Middle East-based official said it was Greek-owned and Comoros-flagged.

The US navy’s 5th Fleet, which is based in Bahrain and oversees anti-piracy efforts in the region, did not respond to a request for comment.

Piracy off Somalia’s coast was once a serious threat to the global shipping industry. It has lessened in recent years after an international effort to patrol near the country, whose weak central government has been trying to assert itself after a quarter-century of conflict.

But frustrations have been rising among fishermen, including former pirates, at what they say are foreign fishermen illegally fishing in local waters.

Salad Nur, an elder in Alula, a coastal town in Puntland, told the Associated Press that young fishermen including former pirates had hijacked the ship.

“They have been sailing through the ocean in search for a foreign ship to hijack since yesterday morning and found this ship and boarded it,” he said. “Foreign fishermen destroyed their livelihoods and deprived them of proper fishing.”

Somali pirates usually hijack ships and crew for ransom. They do not normally kill hostages unless they come under attack, including during rescue attempts.