Hopes of averting a major new conflagration between Iran and the US soon after Tuesday’s midterm elections could rest on Iran’s response to a personal letter from the US vice-president, JD Vance , offering to restart diplomacy.

The letter, written after predominantly Qatari mediation, was sent to the secretary of Iran’s supreme national security council, Mohsen Rezaei on Sunday. It requires Tehran to agree to make commitments on its nuclear programme at the start of a process that would lead to the opening of the strait of Hormuz within seven days in return for US sanctions relief.

A reply is imminent, but Iran is reluctant to give upfront and irreversible commitments on its nuclear programme, such as exporting its stockpile of highly enriched uranium to a third country, if the compensatory US steps, such as lifting sanctions on Iranian oil exports, are reversible.

Some form of third-party guarantee that both sides will adhere to their commitments has been discussed, with China often mentioned as the only…