The seizure of an Iranian oil tanker off the Gibraltar coast by British Royal Marines and the faltering nuclear deal appear to be moving fast towards a head-on diplomatic crash.

On Tuesday, Iran’s hardline media hammered away at the government of President Hassan Rouhani over the seizure of the Panamanian-flagged Grace 1 on 4 July, apparently at the behest of the US.

“The proper response to the UK’s impudence is a counter-response, not summoning the ambassador or posting a tweet,” the hardline newspaper Keyhan said in a bold-faced front-page headline, in a jibe at Mr Rouhani’s foreign minister Javad Zarif, an architect of the Joint Comprehensive Plan of Action (JCPOA) and an accomplished user of Twitter.

Although not linked to the nuclear deal, the seizure of Grace 1 may ultimately undermine those in Tehran advocating a more measured response to the US reimposition of sanctions. The tanker was nabbed just as Iran and world powers were preparing to begin two months of talks that could stop Tehran from further escalating its nuclear programme.

On Tuesday, the foreign ministers of the UK, France and Germany issued a statement voicing “deep concern” that Iran has upped its uranium enrichment levels from 3.67 per cent to 4.5 per cent, and called for the formation of a “joint commission”, as prescribed by the JCPOA, to address the disputes.

Tensions high as Trump approves new Iran sanctions: In pictures Show all 17 1 /17 Tensions high as Trump approves new Iran sanctions: In pictures Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, their surface-to-air missile is seen as it shoots down a US surveillance drone EPA Tensions high as Trump approves new Iran sanctions: In pictures This photo shows US RQ-4A Global Hawk unmanned surveillance drone. A drone of this model was shot down by Iran on Thursday 21 June AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures An oil tanker is on fire after it was subject to a suspected attacked at the Gulf of Oman on June 13. The US has blamed Iran for the attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures US President Trump holds up a signed executive order to increase sanctions on Iran on 24 June AP Tensions high as Trump approves new Iran sanctions: In pictures Iranian President Rouhani stated in a televised address that the White House is "afflicted by mental retardation" following the increase in sanctions on 25 June EPA Tensions high as Trump approves new Iran sanctions: In pictures An Iranian navy boat tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Iran claims that in this picture released by Iran state TV, debris from the downed US drone is seen after it was recovered from Iranian waters AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures A screenshot from a video released by the US Department of Defense that the US claims to show Iranian removing an unexploded limpet mine form the hull of the Japan-owned ship that was attacked in the Gulf of Oman on June 13 Getty Tensions high as Trump approves new Iran sanctions: In pictures An item reportedly found on the Japan-owned oil tanker that was attacked on June 13 in the Gulf of Oman AFP/Getty Tensions high as Trump approves new Iran sanctions: In pictures A handout photograph from the US Department of Defense shows a composite material that the US claim was left behind on the hull of the Japan-owned oil tanker following the removal of an unexploded limpet mine Getty Tensions high as Trump approves new Iran sanctions: In pictures A view from the cabin of an Iranian navy boat as it tackles the fire on the Norwegian owned Front Altair oil tanker after it was hit in a suspected attack EPA Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The picture suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack Reuters Tensions high as Trump approves new Iran sanctions: In pictures Smoke billows from an oil tanker after it was subject to a suspected attacked at the Gulf of Oman on June 13 Reuters Tensions high as Trump approves new Iran sanctions: In pictures Release by US government A picture released by U.S. Central Command shows damage to the hull of the oil tanker Kokuka Courageous. The pictures suggests that the ship is 'likely' to have been hit by a mine as the US Secretary of State Mike Pompeo moves to blame Iran for the suspected attack EPA

French president Emmanuel Macron’s top diplomatic advisor, Emmanuel Bonne, was scheduled to arrive in Tehran on Tuesday to meet with Iranian leaders, a task that could be complicated by the ill will generated by the tanker seizure.

“Release the tanker before negotiating with p4+1,” the hardline Vatan-e Emruz newspaper demanded in a front-page headline alongside a photo of the tanker, referring to the four permanent members of the UN security council and Germany.

Gibraltar authorities said in a press statement issued on Monday that the tanker was loaded with crude oil when it was captured in its territorial waters “during a pre-arranged call for provisions and spare parts” as part of European Union sanctions on prohibitions of exporting crude oil to Syria.

The seizure of the ship creates tangled legal issues that crisscross maritime and sanctions law. It also shows how western policy goals can contradict each other when it comes to Iran.

“Certainly this latest move by the Brits comes during very poor timing in terms of the European outreach with Iran to reverse its non-compliance actions,” said Ellie Geranmayeh, Iran specialist at the European Council on foreign relations.

“If anything it is validating in the eyes of hardliners in Iran what they’ve been saying all along, which is that Europe is playing good cop to Trump’s bad cop ... You can’t but help [seeing this British move], if you’re in Tehran, as a gesture that has been made at the behest of the United States to squeeze Iran further.”

Hardline Iranian newspaper demands: “Freedom of the oil tanker before negotiations with P4+1” (Vatan-e-Emrouz)

Abbas Araghchi, Iran’s deputy foreign minister, insisted on Sunday that the ship was not headed to the Syrian port of Baniyas, which is the location of a refinery. “The port that they have named in Syria essentially does not have the capacity for such a supertanker,” he said. “The target was somewhere else.”

But he did not specify its destination, saying only that it was passing through international waters and “there is no law that allows England to stop this tanker”.

Some experts question whether the EU has the right to apply its sanctions on non-members. Gibraltar authorities say they have received a court order to hold on to the vessel until at least 19 July. The UK, and its overseas territory Gibraltar, will cease to be members of the EU after Brexit.

Iran has been frustrated by its inability to sell oil internationally. The US has warned that it would punish any firm or nation that purchased Iranian energy products, the lifeblood of its economy.

Independent experts believe Iran was behind attacks on half-a-dozen oil tankers transiting from the Arabian Peninsula in response to the US blockade. And Iranian officials have now warned the UK they will respond to the seizure of Grace 1.

“This action will not go unanswered and, if need be, at an appropriate time and place, a response to this miserable action will be considered,” Maj Gen Mohammad Hossein Baqeri, chief of staff of the Iranian Armed Forces, was quoted as saying on Tuesday by the Fars news agency.

Analysts warn that the longer the tanker issue plays out, the more dangerous it will become.

“The longer the situation continues, the more thinking will be done in Tehran about the range of possible responses,” said Ms Geranmayeh.