DUBAI: A Vietnamese-flagged oil tanker, Sothys, has been spotted on Thursday transferring 700,000 barrels of Iranian crude oil to an Iran-flagged tanker, Tankertrackers.com said on Twitter.
Earlier, Vietnam said it was working with Iran to resolve the fate of the tanker seized in the Gulf that sparked diplomatic squabbling between Washington and Tehran.
Iran and the United States gave sharply differing accounts of what happened to the MV Sothys, a Vietnamese-flagged vessel, in the Sea of Oman last week.
Iran's elite Revolutionary Guards (IRGC) said they thwarted an attempt by the US Navy to seize the vessel carrying its oil.
But US defence officials rejected that account, and said that Iran seized the tanker and took it into their waters.
Vietnam's foreign ministry told reporters Thursday that it would "work closely with Iranian competent authorities to resolve this issue".
It said the tanker's captain confirmed to the Vietnamese embassy in Tehran on October 27 that all 26 crew members were in good health and being treated well.
The incident came in the wake of a series of attacks on commercial vessels in the sea lanes serving the Gulf, where a large portion of the world's oil is produced and shipped.
Iran was blamed for a July 29 drone strike on an Israel-linked tanker sailing off the coast of Oman, the MV Mercer Street, in which a former British soldier and Romanian national were killed.
Iran denied that, as well as accusations it was behind other attacks and hijackings in the area.
The argument over last week's tanker incident comes alongside efforts to bring Iran back into talks to restore a broken deal over freezing its nuclear weapons programme.
Iran agreed Wednesday to resume discussions on November 29 with world powers.