The UK and France have signed a joint declaration pledging to deploy troops to Ukraine in the event of a peace deal, to guarantee the nation's security.
The agreement states that a "multinational force for Ukraine" would be deployed to the Eastern European country to deter further attacks from Russia and bolster security guarantees.
This would also allow the Ukrainian armed forces to rebuild strength, Sir Keir Starmer has announced.
It follows a meeting of the Coalition of the Willing in Paris on Tuesday afternoon, led by French President Emmanuel Macron and the British prime minister. Jared Kushner, the US president's son-in-law, and the US special envoy to the Middle East, Steve Witkoff, also attended the talks.
Sir Keir has previously stated that the UK might deploy troops to Ukraine following a peace deal, but this agreement now creates the legal framework for allowing British and French troops to operate there.
The declaration was formally unveiled at a news conference by Mr Macron, Ukrainian President Volodymyr Zelenskyy and Sir Keir.
Addressing the media, Sir Keir said: "We've had a very constructive meeting.
"The purpose of the Coalition of the Willing is to help to deliver a peace that can last and to work with the US to guarantee Ukrainian security for the long term.
"This work is more advanced than ever."
He then laid out the terms of the declaration.
As well as ensuring that soldiers will be deployed on Ukrainian soil, the agreement also covers protection for Ukraine's skies and seas.
The declaration also states that the two countries would establish "military hubs" in Ukraine, so that military equipment could be deployed for defensive needs.
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