US Secretary of State Mike Pompeo pressed Washington's case to extend the UN weapons embargo on Iran in discussions with UK Prime Minister Boris Johnson in London.
Mr Pompeo arrived in the British capital on Tuesday wearing what is becoming his hallmark stars-and-stripes face mask to discuss the security concerns facing the US and Britain.
Standing alongside British Foreign Secretary Dominic Raab, he said he discussed the importance of extending the arms embargo, which is due to expire in October.
“We welcome the recent statement from the UK, France and Germany recognising that allowing the arms embargo to expire would have major implications for regional insecurity and stability,” Mr Pompeo said.
Diplomatic momentum has also been building behind the scenes before a critical UN Security Council decision on whether to extend the 13-year weapons embargo.
The US is applying a policy of maximum pressure on Iran, withdrawing from the 2015 nuclear deal between world powers and Tehran and reimposing crippling economic sanctions.
The extension of the arms embargo could deliver a mortal blow to the deal, which Britain and its European allies are seeking to maintain.
"There's a lot of back-channel momentum between all parties," Dr Sanam Vakil, deputy director of the Chatham House think tank's Mena Programme, told The National. "It's a big priority for the UK."
The US and UK will try to turn the build-up to the October deadline on the Iran weapons embargo to their advantage, Dr Vakil said.
While Britain could look to burnish its post-Brexit credentials as a mediator between continental Europe and the US, Washington could regard the UK as a possible ally at the UN Security Council.
“I think the Americans see the relationship with the UK right now as being one where there can be a bit of give and take on a variety of issues,” Dr Vakil said.
In June, Britain, France and Germany admonished Iran for breaching its commitments under the terms of the nuclear deal and expressed reservations about lifting the arms embargo.
But the three nations also hit out at the US for withdrawing from the deal in 2018, and said they could work with Russia and China, all other Security Council members and other major stakeholders to resolve the impasse.
Ellie Geranmayeh, deputy director of the Mena programme at the European Council on Foreign Relations, said Britain’s track record on Iran in the past year meant it was unlikely to join the US in its policy of maximum pressure.
After the British-flagged Stena Impero was seized in the Strait of Hormuz last year, Britain did not seek to increase tension with Iran.
It also chose not to act when a British military medic was killed at Taji military base, north of Baghdad, in March.
“At that time, there was a push for the UK to come on board, and actually the UK had a much more measured approach,” Ms Geranmayeh said.
With opposition to the embargo extension from Russia, China, Germany and France on the UN Security Council, it is possible the US will acquiesce and allow it to be lifted with restrictive measures.
The could include a code of conduct imposed on Iran over arms sales.
“I do think that there is a way to moderate the response from Iran by having this code of conduct, which means that they are not locked into a UN Security Council arrangement,” Ms Geranmayeh said.
