The British government has not given the United States consent to use military facilities on the country's territory for possible strikes against Iran, the BBC reported.
In the past, US forces have used RAF Fairford in Gloucestershire and the Indian Ocean island of Diego Garcia - part of the British overseas territories - for operations in the Middle East.
According to a report in The Times, London's refusal has led to new criticism from US President Donald Trump, including in connection with the agreement to return the Chagos Islands to Mauritius and the extension of the lease of Diego Garcia, where a joint British-American base is located. The British government said it generally does not comment on operational matters.
Washington has been pressuring Tehran to curb its nuclear program and has warned of possible military action if progress is not made. US warships, aircraft and other forces are already in the region in preparation for a potential operation.
Meanwhile, talks between US and Iranian officials in Switzerland have been reported to have made some progress. On Thursday, Trump said it would be clear within about ten days whether a deal would be reached or military action would follow. London has stressed its support for the diplomatic process and that Iran should not be allowed to develop nuclear weapons, with regional security remaining a top priority.