Senior military officers from the “coalition of the willing” are meeting in private in the UK on Thursday to discuss plans for a potential peacekeeping mission for Ukraine.
It is believed that almost 20 nations are participating.
Prime Minister Sir Keir Starmer is anticipated to attend on Thursday afternoon after visiting Barrow, where he will lay the keel for one of Britain’s new generation of nuclear-armed submarines.
Plans for a Western-led peacekeeping force for Ukraine are said to be moving to an operational phase.
Senior military officers from nations that make up the “coalition of the willing”, led by Britain and France, are due to discuss how this would work in practice when they gather at the UK’s Permanent Joint Headquarters in Northwood.
Armed Forces minister Luke Pollard said they want the coalition to be a “credible force” that would allow Ukraine to “enjoy a lasting peace” and “reconstitute and rearm”.
Pollard said securing peace in Ukraine may mean “some boots on the ground”, but the force will also “have a strong feature of air and maritime forces”.
Russian President Vladimir Putin has said Moscow will not tolerate the presence of any Nato member troops in Ukraine, regardless of their role.
The US is also proving reluctant to provide the necessary air cover that prospective members say they need.
Sir Keir is expected to attend part of the meeting after first visiting Barrow where he will lay the keel of HMS Dreadnought, one of the next generation of nuclear-armed submarines.
On his visit to the town, Sir Keir will say Barrow is a “blueprint” for how defence spending can benefit a community.
He is due to announce that the King has agreed to grant Barrow the title of “Royal” in recognition of its contribution to national security.
Earlier, he visited the crew of one of Britain’s nuclear submarines, HMS Vanguard, as it returned to Scotland after patrolling the waters of the north Atlantic.
The prime minister told reporters the Kremlin respected the UK’s nuclear arsenal because “we’ve got our own independent deterrent and we’re committed to Nato”.
