Sir Keir Starmer has called on Iran to "return to the negotiating table" after the US bombed nuclear sites in the country overnight.
In a statement, the UK prime minister said stability in the region was a priority, describing Iran's nuclear programme as "a grave threat to international security".
The BBC understands there was no UK involvement in the US strikes on Iranian nuclear facilities and that the prime minister was informed of them in advance.
"Iran can never be allowed to develop a nuclear weapon and the US has taken action to alleviate that threat," Starmer added.
The US said it had carried out strikes on three nuclear facilities in Iran: Natanz, Isfahan and Fordo on Saturday night.
