British Prime Minister Keir Starmer has indicated that Ukraine can use long-range missiles supplied by the UK to strike military targets in Russia during their war.
Mr Starmer told reporters on his flight to Washington for NATO's 75th anniversary summit that decisions on the use of British-supplied Storm Shadow missiles were for the Ukrainian armed forces.
UK military aid is "for defensive purposes but it is for Ukraine to decide how to deploy it for those defensive purposes", said Mr Starmer.
The comments confirm that Labour is pursuing the same stance on the air-launched missiles as the previous Conservative governments led by Rishi Sunak, Liz Truss and earlier Boris Johnson.
Britain has been one of Kyiv's staunchest allies since Russian President Vladimir Putin launched a full-scale invasion of neighbouring Ukraine in February 2022.
The UK has provided money, weapons and troop training to Ukraine's fight.
Britain was the first country to provide longer-range weapons to the Ukrainian military, announcing last May that it would send Storm Shadow missiles.
Mr Starmer was due to reaffirm Britain's support for Ukraine and its "unshakeable commitment" to the western military alliance NATO during the summit, where he is due to meet Ukrainian President Volodymyr Zelensky.
Mr Starmer is also due to meet US President Joe Biden are due to meet at the White House.
Both leaders are expected to discuss a range of issues such as support for Ukraine and the need to achieve a ceasefire in Gaza.
Mr Starmer's visit to the White House is seen as a diplomatic coup during his first week in office.
But the summit comes with Mr Biden mired in domestic political difficulties and with the prospect of Donald Trump replacing him in the White House after November's election and adopting a much more sceptical approach to NATO.
Mr Trump has repeatedly called for European nations to ramp up defence spending if they want to continue to enjoy the protection of the US as part of the alliance.
Mr Starmer has confirmed that the UK government is set to launch a Strategic Defence Review which will set out a roadmap to spending 2.5% of UK GDP on defence.
He will hope he can persuade more countries to meet the alliance's target of spending 2% of GDP on defence, even as he faces pressure to spell out more details of his own 2.5% commitment.
Mr Starmer arrived in Washington yesterday for the NATO summit.
NATO leaders will also have the opportunity to discuss UK-US cooperation on advancing a free and open Indo-Pacific, reaching a ceasefire and hostage release deal in Gaza, Iran and the threat of Houthi rebels to commercial shipping.
The gathering in Washington comes just days after a Russian missile struck a children's hospital in Kyiv.
Additional reporting Tommy Meskill, PA
