Iran says it will soon release a British-flagged tanker that its Revolutionary Guards seized more than two months ago, sparking a crisis in Gulf shipping.

Maritime authorities in the Islamic republic told the semi-official Fars news agency on Sunday that the Swedish-owned Stena Impero would imminently be released, confirming earlier remarks by the chief executive of Stena Bulk, the company that owns the vessel.

“We received information this morning indicating that the ship Stena Impero is going to be released in a few hours,” Erik Hanell, chief executive at Stena Bulk, told Swedish television SVT on Sunday.

The Stena Impero was dramatically seized on 19 July as it passed through the strait of Hormuz after Iranian officials claimed it had infringed maritime regulations. Footage released by Iran showed Revolutionary Guards descending from a helicopter to take control of the ship and detain its 23 crew members.

About two weeks earlier, British Royal Marines seized an Iranian supertanker off the coast of Gibraltar carrying 2.1m barrels of crude oil that UK authorities alleged was to be sold to Syria in breach of EU sanctions against Bashar al-Assad’s government. Iran has denied the Stena Impero’s impoundment was a tit-for-tat move.

The takeover, which led the UK to advise its ships to temporarily avoid the strait of Hormuz, was part of a wave of sabotage attacks and seizures of ships over the past six months in and around the narrow waterway through which more than a quarter of the world’s oil supply passes.

The US and Gulf states have blamed Iran for the incidents including the alleged use of explosives against four oil tankers in the Gulf of Oman in May, suspicious fires on two tankers in the same area in June and the attempted seizure of the British vessel in July, allegedly by Iranian boats that were driven off by a Royal Navy warship.

A Gibraltar court ordered the release of the Iranian vessel, then called Grace and since renamed Adrian Darya 1, on 18 August after receiving written assurances from Iran that it would not head to countries under EU sanctions.

Tehran denies making any such assurances and the UK says the Adrian Darya 1, which turned off its transponder off the Syrian coast earlier this month, has sold its oil to Assad’s regime. Satellite images of the ship said to have been taken days after it stopped transmitting its location showed it near the Syrian port of Tartus.

Iran’s envoy to London claims the cargo was sold to a private company in a ship-to-ship transfer. The Islamic republic’s oil exports have fallen from around 2m barrels per day in August 2018 to around 160,000 barrels per day after the US imposed sanctions on the industry in November.

Washington is seeking to force Tehran to negotiate a new nuclear deal to replace the 2015 agreement that Donald Trump unilaterally pulled out from in May last year.

Trump said the deal, which traded curbs in Iran’s nuclear program for relief from sanctions, needed to also address Iranian missile development, human rights abuses and sponsorship of proxies. Iran had been in full compliance with the agreement when it was breached by the US.

The incidents in the strait of Hormuz have led the US to create the international maritime security construct, an alliance of countries including Bahrain, Australia and the UK whose vessels are trying to deter Iranian intervention against oil tankers in the area.

Saudi Arabia and the UAE have both signed up to the construct in the past week since an attack on Saudi oil facilities that the kingdom said involved Iranian-made weapons.