British officials said they were not ready to comment on what they could promise to the 300,000-strong force.
The news came as NATO leaders discussed the alliance’s most significant defensive overhaul since the end of the Cold War.
The organization pledged “steadfast” support to Ukraine in the face of Russian aggression, the root cause of the policy shift.
Volodymyr Zelensky, Ukraine’s president, warned via a video link at the summit on Wednesday that it would be seen as a collective failure if Moscow is not defeated within a year.
He called for more Western weapons and financial support, and the cost of defending his country against Russia is estimated at more than £4 billion a month.
He said that without enough support for Kiev to end the war before the end of the year, NATO leaders risked the vicious conflict spilling over into the alliance.
“Next year, the situation could be worse – if not only Ukraine, but also several other states, possibly members of the alliance, come under fire from Russia. And then it will be our common failure – Ukraine and NATO,” he added.
Zelensky said he needed more weapons to break Russia’s artillery advantage in the brutal battle for the Donbas.
In a clear message to NATO leaders, Mr Zelensky called on them to find a place for Ukraine in Europe’s Common Security Area.