Both Defence Secretary John Healey and Mr Lammy said this week they would not publicly discuss the details of the talks with the US because “such a debate would benefit Putin”.

Other Western allies expressed concern about the supply of Iranian long-range missiles to Russia.

EU foreign policy chief Peter Stano said the move was “likely to support Russia’s escalating bombing campaign against Ukrainian civilians.”

“Such support for Russia’s terror campaign against the Ukrainian people will be met with a strong reaction from the EU,” he said.

The Iranian Foreign Ministry said that “all allegations that the Islamic Republic of Iran has sold ballistic missiles to the Russian Federation are completely baseless and false” and said it would respond to the sanctions with a “proportionate response.”

Sir Keir’s visit to Washington on Friday is his second since taking office in July. A few days after taking office, he met Biden on the sidelines of a NATO summit at the White House.

At the summit, he suggested Storm Shadow restrictions could soon be lifted, which delighted Mr Zelensky. Downing Street later clarified that the UK government’s policy had not changed.