Foreign minister Jeremy Hunt said he told his Iranian counterpart on Saturday that Britain would facilitate the release of the detained Grace 1 oil tanker if there were guarantees it would not go to Syria.

Hunt said Iranian foreign minister Mohammad Javad Zarif had told him that Iran wanted to resolve the issue and was not seeking to escalate tensions.

He tweeted: “Just spoke to Iranian Foreign Minister Zarif. Constructive call. I reassured him our concern was destination not origin of the oil on Grace One & that UK would facilitate release if we received guarantees that it would not be going to Syria, following due process in Gib courts.

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“Was told by FM Zarif that Iran wants to resolve issue and is not seeking to escalate. Also spoke to [Gibraltar’s chief minister] Fabian Picardo who is doing an excellent job co-ordinating issue and shares UK perspective on the way forward.”

The exchange comes after confirmation that the UK will step up its military presence in the Gulf by sending a second warship to the region to protect British commercial oil tankers.

HMS Duncan, a Type 45 destroyer, will be deployed within days after it completes a course of Nato exercises in the Baltic Sea, with the aim of being in the Gulf region by next week.

The ship will work alongside the Royal Navy’s frigate HMS Montrose and US Gulf allies, but will not participate in Washington’s proposed global maritime coalition to protect shipping in the area.

Theresa May said this week that she would begin talks with US authorities on increasing a transatlantic presence in the region, following two sets of attacks on oil tankers in the Gulf of Oman and an attempt by the Iranian navy to push a British-owned oil tanker towards Iranian waters.

In a statement, Hunt said that during a phone call with Gibraltar’s chief minister, Fabian Picardo, they “agreed the importance of deescalating the current situation as quickly as possible while noting the importance of Gibraltar enforcing EU sanctions against Syria through its legal processes”.

He added: “Mr Picardo noted that Gibraltar would be prepared to facilitate, subject to its obligations under EU law, the release of the detained assets to a rightful claimant if they were satisfied that they had received guarantees it would not be going to Syria.

“The detention and investigation of the Grace 1 has been – and continues to be – – a government of Gibraltar-led operation to uphold EU sanctions on Syria. I pay tribute to the admirable leadership of the chief minister throughout this process, ably supported by Gibraltarian authorities.”

Hunt said that during his phone call with Zarif, he reiterated how the decision to detain the Grace 1 related to the destination of the vessel and not to its origin.

“This was about the enforcement of EU Syria sanctions: action was taken because of where the oil was going – a sanctioned Syrian entity – – not because it was from Iran,” he said.

Britain’s relations with Iran deteriorated last week when the UK seized Grace 1, suspected to be carrying oil destined for Syria, in breach of EU sanctions. Tehran has denied the ship was heading for Syria and threatened to seize a British oil tanker in retaliation if Grace 1 was not released.

The ship’s captain and chief officer were arrested by the Gibraltarian authorities after the vessel was searched for more than a week. On Saturday, the Royal Gibraltar police said the pair and two second officers had been conditionally bailed without charge, while the investigation is continuing and the vessel remains in detention.