Joe Biden is poised to lift a ban on British Storm Shadow missiles being fired into Russia by Ukraine.
The president is considering changing policy after it emerged Iran is now arming Russia with ballistic missiles, which could be used in Ukraine within weeks.
Antony Blinken, Mr Biden’s secretary of state, is due in Ukraine on Wednesday with David Lammy, the Foreign Secretary, to discuss lifting restrictions with Volodymyr Zelensky.
Mr Biden and Sir Keir Starmer would then discuss changing the policy in a White House summit on Friday, Mr Blinken said, adding that the president was “not ruling it out”.
The delivery of new Iranian arms to Russia is thought to have prompted fresh discussions between the US and UK over the use of Storm Shadows.
“Russia has now received shipments of these ballistic missiles and will likely use them within weeks in Ukraine against Ukrainians,” Mr Blinken said on a visit to London on Tuesday.
“This is a threat, not only to Ukraine and the Ukrainian people, but to all of Europe.”