Ukrainian President Volodymyr Zelenskiy travels to London to meet Prime Minister Rishi Sunak and address parliament on Wednesday at a time when Kyiv is urging the West to deliver more weapons to try to reverse Russian gains.

In only his second foreign visit since Russia invaded Ukraine on Feb. 24 last year, Zelenskiy will visit troops working with British forces, part of a programme Sunak will say he plans to expand to include the training of fighter jet pilots and marines.

"President Zelenskiy's visit to the UK is a testament to his country's courage, determination and fight, and a testament to the unbreakable friendship between our two countries," Sunak said in a statement.

"I am proud that today we will expand that training from soldiers to marines and fighter jet pilots, ensuring Ukraine has a military able to defend its interests well into the future."

Britain will also set out further sanctions later on Wednesday to target those who have helped Russian President Vladimir Putin "build his personal wealth, and companies who are profiting from the Kremlin’s war machine", the statement said.

Zelenskiy, who had close ties with ex-prime minister Boris Johnson, visits Britain at a time when Russia is bringing tens of thousands of recently mobilised troops to the battlefield to try to break through Ukrainian defences in eastern Ukraine.

Ukraine expects Russia to launch a major new offensive before Kyiv can start using tanks and other weaponry promised by its Western partners.

Since Johnson resigned last year, Sunak has pledged to continue to support Ukraine, visiting Kyiv in November to tell the Ukrainian leader: "We are with you all the way."

In London, he is expected to tell Zelenskiy he will accelerate delivery of military equipment to Ukraine.

Ukraine's allies have pledged to give Ukraine hundreds of tanks and armoured vehicles to help it break through Russian lines and recapture territory, but the country's military need time to train its forces in how to use them effectively.

Britain has trained 10,000 Ukrainian troops brought to battle readiness in the last six months and will upskill a further 20,000 soldiers this year, the government said.

Last week, Ukrainian troops arrived in Britain to learn how to command Challenger 2 tanks and Sunak will offer to provide Ukraine with longer range capabilities, the statement said. (Reporting by Muvija M and Elizabeth Piper; editing by William James and Kate Holton)