Live updates: Follow the latest news on US-Iran war
Iran fired two long-range missiles at the joint UK-US military base on Diego Garcia after Tehran threatened retaliation against British targets.
US officials reportedly confirmed that the ballistic missiles were aimed at the Indian Ocean territory with a US warship taking out one of the projectiles in flight.
Britain said late on Friday US bombers taking off from UK airbases could hit Iranian military operations that were attacking ships moving through the Strait of Hormuz.
Iranian Foreign Minister Abbas Araghchi criticised Prime Minister Keir Starmer in a series of social media messages on Friday. After the announcement of additional permissions, he invoked Iran's right to self-defence. "Mr Starmer is putting British lives in danger by allowing UK bases to be used for aggression against Iran," he said.
UK ministers said Iran's "reckless strikes" around the Arabian Gulf risked the security of the region as well as worsening the economic impact of the war being felt in the UK and the world.
Foreign Secretary Yvette Cooper warned Iran against attacking UK interests after Tehran said the use of Deigo Garcia and RAF Fairford airbases was “participation in aggression”.
Ms Cooper said UK operations in the region were in response to Iran’s strikes on Gulf countries.
Military experts said on Saturday that range of the missiles exceeded the known capability of Iran's ballistic missiles. From Iran to Diego Garcia is a distance of 3,800 kilometres, while it was thought the maximum range of Iranian missiles was 2,000km.
Gen Sir Richard Barrons told the Radio4 Today programme that British interests were in Iran's sights. "We may not have wanted to get involved but now we are involved."
Iranian retaliation
Mr Araghchi hinted at retaliatory action in his version of the call with Ms Cooper. “These actions will definitely be considered as participation in aggression and will be recorded in the history of relations between the two countries,” he said.
“At the same time, we reserve our inherent right to defend the country’s sovereignty and independence.”
The spat comes as concerns grow over Iran's sleeper network of agents in Europe as well as its capacity to strike at the UK sovereign bases in Cyprus, which was hit in the early days of the war.
An Iranian man was charged on Saturday after he arrested on Thursday close to the entrance to the base housing the UK's nuclear deterrent near Glasgow. The 34-year-old and a 31-year-old Romanian woman had been turned away from the entrance and then held for acting suspiciously near the gate.
The naval base at Faslane is home to the core of the UK’s submarine fleet and the Trident nuclear deterrent.
Nato retreat
Further afield, Nato said it had relocated all its personnel from a training mission in the Middle East to Europe. “I would like to thank the Republic of Iraq and all the allies who assisted in the safe relocation of Nato personnel from Iraq,” Gen Alexus Grynkewich, the commander of the alliance, said.
The bases in northern Iraq were attacked by Iran and local militias sympathetic to Tehran.
US President Donald Trump condemned Nato members for snubbing his call for direct intervention to open the Strait of Hormuz. He called his alliance partners cowards in a social media message.
Defensive permission
Mr Starmer stressed US permission for “defensive” action against Iranian missile sites from RAF Fairford in Gloucestershire and Diego Garcia in the Indian Ocean.
The Foreign Office said that Ms Cooper had condemned Iran’s “reckless attacks” on Gulf partners during the Friday call with Mr Araghchi.
“The Foreign Secretary also warned Iran against targeting UK bases, territory or interests directly and restated the UK’s focus on regional stability and security.”
