British boots on the ground: What could a UK-Europe force in Ukraine look like?

Protecting Ukraine's skies and coastline will also be key.

The officials declined to give numbers on the size of any potential force but signalled it would be under 30,000 personnel.

Sir Keir Starmer will reportedly discuss the plan with Donald Trump when the two meet in the US in the coming days.

Soldiers would not be posted close to frontline areas in the east and they would not be operating as "peacekeepers".

Instead, the officials indicated that they would be a "reassurance" force for the public and to help encourage the return of millions of Ukrainians who fled the country because of Russia's war.

This - should any such deployment be agreed - could include troops being located in major cities, ports and at sites of critical national infrastructure, such as nuclear power plants.

Satellites, spy planes and drones could also help in the effort.

Fleshing out details of ideas that are being discussed among European allies, led by the UK and France, it is understood that there could also be a kind of air policing-style mission, using fast jets based outside Ukraine, to assist with reopening Ukrainian airspace to civilian passenger planes once again.

No civilian flights have been possible since the start of Vladimir Putin's full-scale war.

The UK and other NATO countries already perform this task in the Baltic states and Romania, patrolling the airspace to deter threats.

In addition, deploying warships to the Black Sea is a possibility, with the need for demining efforts as well as patrols to aid the resumption of maritime traffic off the Ukrainian coast.

Volodymyr Zelenskyy, the Ukrainian president, has already said the Royal Navy would be a good partner to help secure Ukraine's shipping lanes along with its Nordic allies.

However, any kind of European-led reassurance mission would only work if there is what Sir Keir has described as a US "backstop".

He has not elaborated on what that means but it is thought US involvement is vital to deliver the deterrent effect to ensure that Russia would not try to re-attack Ukraine for fear of triggering a US response.

This backstop could involve American military aircraft based outside Ukraine.

Donald Trump has not said whether he would support any such operation, while his defence secretary, Pete Hegseth, has categorically ruled out any American troops being sent to Ukraine.

For its part, Russia has said the deployment of any European or NATO forces in Ukraine would be "unacceptable".

Ukraine's president has previously said any international security force would have to be about 110,000-strong.

But the Washington Post reported that discussions among European allies envisaged a contingent of between 25,000 and 30,000 personnel.

Speaking on Wednesday, Mr Zelenskyy said his country would need security guarantees provided by its NATO partners.

Or it would need financing and weapons to build its own one-million-strong army, backed by a "comprehensive air defence system".

He was referring to the US Patriot system, saying if Washington would not give Kyiv any more of these, perhaps it would be possible to buy them or receive a licence to build them in Ukraine.

"Ukraine is in a situation where we do not have many security guarantee options available," Mr Zelenskyy said. "Creating something entirely new, something global, is unrealistic. We need security guarantees this year because we want to end the war this year."

-SKY NEWS