A United Nations agency has acknowledged that a US-sought oil tanker "hijacked" off the coast of the United Arab Emirates (UAE) after allegedly smuggling Iranian crude oil is back in Iranian waters.

The International Labour Organization (ILO) on Sunday said the MT Gulf Sky was hijacked on July 5, citing its captain. That mirrors earlier reporting by The Associated Press news agency.

"The vessel was taken to Iran," the ILO said. All 28 Indian crew members disembarked in Iran and all but two of the crew without passports flew from Tehran to India on July 15, it added.

The ILO cited the International Seafarers' Welfare and Assistance Network for its information. The agency earlier filed a report saying the vessel and its sailors had been abandoned by its owners without pay since March off Khorfakkan, a city on the eastern coast of the UAE.

Iranian state media and officials have not acknowledged the hijacking and arrival of the MT Gulf Sky to Iran. The United States government similarly has not commented.In May, the US Justice Department filed criminal charges against two Iranians, accusing them of trying to launder some $12m to buy the tanker, then named the MT Nautica, through a series of front companies.