Britain and Europe have warned Donald Trump that any US attack on Iran risks endangering Westerners being held by the Islamic Republic.
Diplomatic sources told
The Telegraph that Washington had also been told that military intervention could trigger a wave of terror attacks by sleeper cells across Europe.
It comes as part of an effort by Britain, France and Germany to broker a diplomatic end to Israel’s war with Iran.
Mr Trump has approved plans for a US strike on Iran, but has not yet given a final order.
European foreign ministers will meet their Iranian counterpart for talks in Geneva, Switzerland, on Friday.
David Lammy, Jean-Noel Barrot and Johann Wadephul will be joined by Kaja Kallas, the EU’s top diplomat, for what could emerge as showdown negotiations to avoid an all-out war in the Middle East.
As the conflict between Israel and Iran continued to escalate on Thursday, Sir Keir Starmer called for “cool heads and a return to diplomacy”. The Prime Minister’s spokesman added: “We would not want to see anything that ramps up the situation.”
Emmanuel Macron, the French president, issued a similar plea, calling for an urgent end to Israel’s war to bring Mr Trump back from the brink of becoming involved.
Mr Macron also told aides that he believed Israel’s bombing campaign had moved beyond its original targets of Iran’s nuclear production and ballistic missile facilities.
The talks in Geneva on Friday are aimed at kick-starting a diplomatic process in coordination with Washington and Tehran before any further escalations.
A source told The Telegraph that the UK, France, Germany and EU had all urged restraint from Washington because of a possible threat to detainees held by the Islamic regime.
Two British nationals, a man and a woman, were arrested in Iran in February and accused of security-related offences. In recent years, at least 15 people with links to the UK have been arrested in the country and accused of espionage offences.