British Prime Minister Rishi Sunak has promised 125 anti-aircraft guns and other air-defence technology as he made an unannounced visit to Ukraine's snow-blanketed war-time capital for talks with Ukrainian President Volodymyr Zelenskyy.
The air-defence package, which Britain valued at 50 million pounds ($89 million), comes as Russia has been pounding Ukraine's power grid and other key infrastructure from the air, causing widespread blackouts for millions of Ukrainians amid frigid weather.
The package includes radar and other technology to counter Iran-supplied exploding drones that Russia has used against Ukrainian targets. It comes on top of a delivery of more than 1,000 anti-air missiles that Britain announced earlier this month.
The UK has been one of the staunchest Western supporters of Ukraine's resistance to Russia's invasion, giving Kyiv 2.3 billion pounds in military aid. Mr Zelenskyy described the two countries as "the strongest of allies."
Video that Mr Zelenskyy posted on Saturday showed him greeting Mr Sunak for his first visit to the presidential palace, as snowflakes fell and the two men holding talks.
"With friends like you by our side, we are confident in our victory. Both of our nations know what it means to stand up for freedom," the Ukrainian leader said on social media.
Former UK Prime Minister Boris Johnson, who stepped down in July amid ethics scandals, won wide praise in Ukraine for his backing and made repeated visits to Kyiv.
Mr Sunak is keen to reassure Ukraine's leaders that there will be no change of stance under his leadership, although when he was UK Treasury chief under Mr Johnson he was considered resistant to demands for higher defence spending.
"The courage of the Ukrainian people is an inspiration to the world," Mr Sunak said in comments alongside Mr Zelenskyy in the presidential palace.
"In years to come, we will tell our grandchildren of your story."
He pledged that Britain would "stand with you until Ukraine has won the peace and security it needs and deserves and then we will stand with you as you rebuild your great country."
Mr Sunak also laid flowers at a memorial for the war dead, lit a candle at a memorial for victims of a deadly Soviet-era famine in Ukraine in the 1930s, and met first responders at a fire station, his office said.
The prime minister said it was "deeply humbling" to visit Kyiv "and to have the opportunity to meet those who are doing so much, and paying so high a price, to defend the principles of sovereignty and democracy."