UK leader Rishi Sunak travels to Warsaw on Tuesday for talks with Polish premier Donald Tusk and Nato chief Jens Stoltenberg that will focus on Ukraine and wider European security.
While in Poland's capital, the British prime minister will announce £500 million ($617 million) in additional military funding for Kyiv in its more-than two-year battle against Russia's full-scale invasion, his Downing Street office said in a statement.
"Defending Ukraine against Russia's brutal ambitions is vital for our security and for all of Europe. If Putin is allowed to succeed in this war of aggression, he will not stop at the Polish border," Sunak said ahead of the trip.
His visit to Eastern Europe comes as Kyiv pleads with allies to ramp up supplies of ammunition and air defences desperately needed to repel Russian attacks.
It also takes place as Western countries come under pressure to boost spending on their own defence in the face of Russian threats.
Ukraine has for months struggled with a growing shortage of ammunition, with Europe struggling to provide weaponry as Ukrainian forces get pushed back along the front line.
US lawmakers eased the pressure last weekend by unblocking a $61-billion military aid package for Kyiv following six months of political wrangling.
But EU defence and foreign ministers insist that Europe must still speed up its deliveries of arms to Ukraine.
Germany has answered Kyiv's call in recent days by saying it would send an extra Patriot air defence system to Ukraine.
Stoltenberg said last week that he expected more NATO countries to make announcements on fresh air defences for Kyiv "soon".
During his trip, Sunak will announce the UK's "largest-ever single package of equipment" for Ukraine's war effort.
