An Iranian tanker caught in the standoff between Tehran and the West shifted position on Friday but its anchor was still down off Gibraltar and it was unclear if it was ready to set sail, a Reuters reporter has said.
Gibraltar authorities could not be reached for comment.
The Grace 1 was seized by British Royal Marines at the western mouth of the Mediterranean on July 4 on suspicion of violating European Union sanctions by taking oil to Syria, a close ally of Iran.
Gibraltar lifted the detention order on Thursday but the vessel's fate was further complicated by the United States, which made a last-ditch legal appeal to hold it.
A Reuters reporter in Gibraltar said the vessel appeared to be moving and more smoke could be seen coming from the funnel than in recent days. However it was not clear that the ship was actually leaving and it still appeared to be at anchor.
Refinitiv data did not show the vessel moving.
Earlier the first minister of Gibraltar said the tanker was free to leave as soon as it had organised its logistics.
"Could be today, could be tomorrow," Gibraltar's First Minister Fabian Picardo told BBC Radio.
Washington has attempted to detain the Grace 1 on the grounds that it had links to Iran's Islamic Revolutionary Guard Corps, which it has designated a terrorist organisation.