Prime Minister Keir Starmer is expected to tell a summit in Armenia of the European Political Community - a discussion forum set up after Russia's invasion in 2022 - that Britain wants to work with the EU to support Ukraine in getting vital military equipment, his office said.
The loan, approved by the EU in April, is set to cover two-thirds of Ukraine's needs for the next two years, with the bulk of that amount earmarked for military spending as Kyiv defends itself against Russia's four-year war.
The extra funding could also unlock opportunities for British businesses to meet Ukraine's urgent needs, particularly in the defence sector, the UK government said in a statement.
Britain, which has imposed wide-ranging sanctions on Russia since the war began in 2022, will also announce another tranche of "stinging sanctions" on Russian companies this week to disrupt military supply chains, it said.
Starmer's visit, the first by a British leader to Armenia since former prime minister Margaret Thatcher in 1990, comes as the Trump administration pushes Europe to take more responsibility for the continent's defence.
European countries, including Germany, France and Britain, have recently come under further pressure from Washington after refusing to join the US and Israel's war on Iran.
"When the UK and the European Union work together, we all reap the benefits - and in these volatile times we need to go further and faster on defence to keep people safe," Starmer said in the statement.
He has previously called for stronger defence integration within the continent to cut NATO's over-reliance on the US, hinting at further alignment with the EU's single market and deeper economic integration, six years after Brexit.
Earlier, Ukraine launched a wave of drone attacks on targets across Russia, hitting the Baltic Sea port of Primorsk and setting it on fire, and striking a number of vessels, as it stepped up attacks on energy infrastructure and other targets.
Ukraine's President Volodymyr Zelenskiy said the strikes had caused significant damage to the oil terminal port. They also hit an oil tanker, a small Russian Karakurt-class missile ship and a patrol boat in the Baltic Sea, he said on Telegram.
"Each such result further limits Russia's war potential," he wrote.
Alexander Drozdenko, governor of the northwest region which hosts the port, said more than 60 drones were downed overnight. He said the fire at Primorsk, a major oil-exporting outlet, was quickly extinguished and there had been no oil spill following the attack.
Among numerous reports of other attacks elsewhere in Russia, the governor of the Belgorod region bordering Ukraine, Vyacheslav Gladkov, said a drone had hit a car, killing a 21-year-old man and his father on the spot.
Zelenskiy earlier on Sunday said Ukrainian forces also struck two shadow-fleet tankers in waters at the entrance to the Russian Black Sea port of Novorossiysk.
"These tankers had been actively used to transport oil - not anymore," Zelenskiy said on Telegram.
"Ukraine's long-range capabilities will continue to be developed comprehensively - at sea, in the air, and on land."
Kremlin spokesman Dmitry Peskov said global oil prices may rise further if Ukraine continues to hit Russia's oil infrastructure, Russian TV reported.
Moscow regional governor Andrei Vorobyov said on Saturday evening that a 77-year-old man had died in a village following a drone strike. And Sergei Sobyanin, mayor of the city of Moscow, said four drones were downed on their way to the Russian capital.
Vasily Anokhin, governor of the western Smolensk region, said three people, including a child, were injured on Sunday after a drone attacked an apartment block there.
Russian troops were meanwhile inching towards the city of Kostiantynivka in Ukraine's eastern Donetsk region, Ukraine's top army official said on Saturday.
