An Iranian government spokesman said on Monday that all legal steps had been completed for the release of the detained British-flagged tanker Stena Impero, ending a two-month standoff.
"The legal work and administrative procedures for the release of the English tanker have been completed but I have no information on the time of the release," said government spokesman Ali Rabiei, according to the semi-official news agency.
The ship was seized on July 19, two weeks after Britain detained an Iranian tanker off Gibraltar, cranking up tensions in the region in the wake of attacks on other merchant vessels that Washington blamed on Tehran.
Iran denied responsibility for those attacks, which took place along a vital international oil shipping route.
The semi-official Fars news agency quoted Rabiei as saying: "The legal work for the oil tanker is over ... and the oil tanker can move, and the decisions indicate the end of the detention." He did not elaborate.
Relations between the United States, its allies and Iran have been gradually more strained since Washington withdrew last year from a global pact aimed at reining in Tehran's nuclear programme and imposed sanctions on it aimed at shutting down Iranian oil exports.
The head of the Swedish firm that owns the vessel said earlier on Sunday that the tanker may be released within hours.
Swedish public broadcaster SVT quoted Stena Bulk Chief Executive Erik Hanell as saying: "We have received information now this morning that it seems like they will release the ship Stena Impero within a few hours. So we understand that the political decision to release the ship has been taken."
"We hope to be able to head out within a few hours, but we don't want to anticipate events. We want to see that the ship sails out of Iranian territorial waters," Hanell told SVT, adding that his information came from Iranian authorities.
Hanell late on Sunday told Reuters he had just arrived in Iran. "Unfortunately no further development but we keep at it and hope for a solution within the near future," he said in a text message.
Stena Bulk spokesman Will Marks earlier on Sunday said the vessel was still being held and negotiations were ongoing.
"Until we have official confirmation and the vessel is lifting up its anchor and sailing out of Iranian waters we can't confirm anything else," he told Reuters.
In an update late on Sunday, Marks said the situation remained the same. "We have had no official confirmation of a release yet," he said.
On September 4, Iran released seven of the vessel's 23 crew members. Swedish Foreign Minister Margot Wallstrom said at the time that Sweden had been in daily contact with Iran at a high political level since the vessel was seized.
Britain called on Iran to release the ship and its remaining crew immediately.
"Iran's illegal seizure of a ship inside an internationally recognised shipping lane is unacceptable and undermines international law," a spokesperson for the British government said in an email.