The PM saw them last weekend in the North East and told President Zelensky about it in a call yesterday.
Mr Sunak said he was “inspired by their courage and the stories of their loved ones back home.”
And he told the Ukrainian leader that the troops paid tribute to Mr Zelensky’s “strong leadership”.
The PM vowed to make sure British kit, including newly donated Challenger 2 tanks, get there as quickly as possible.
Number 10 revealed Ukrainian soldiers had already begun training on them.
Meanwhile, the bodies of two British aid workers killed in Ukraine have been recovered.
Andrew Bagshaw, 48, of Truro in Cornwall, and New Zealand resident Chris Parry, 28, died last month while they evacuated civilians in Soledar.
A shell hit their car as they tried to rescue an elderly woman from the Russian onslaught.
The bodies were returned to Ukrainian officials yesterday.