Wallace joined NATO Secretary General Jens Stoltenberg to observe the training of Ukrainian troops in the southeast English town of Lydd, as Britain announced the delivery of a further 12,000 extreme cold-weather sleeping kits for Ukraine.

"Winter is approaching and that is an important challenge for both sides," Wallace said. "So we're determined ... to give Ukrainian soldiers the best basic skills because we already know that the Russian military aren't doing that."

Later, Britain's Ministry of Defence said it would soon complete the delivery of 1,000 additional surface-to-air missiles to Ukraine's armed forces. The equipment includes launchers and missiles and is capable of shooting down air targets including Russian drones and cruise missiles, it said.

Russian Defence Minister Sergei Shoigu on Wednesday ordered his troops to withdraw from the west bank of the Dnipro River in the face of Ukrainian attacks near the southern city of Kherson, a significant retreat and potential turning point in the war.

Ukraine reacted with caution to the announcement, saying some Russian forces were still in Kherson.

Speaking before the announcement from Shoigu, Wallace said Ukraine's advances in the region were why it was so important to maintain the supply of equipment and support.

"Ukraine is still making gains in the east of the country, and slowly but surely closing in on Kherson in the south. That's a tough fight," he said.

Stoltenberg, who said other NATO allies were also providing support to Ukrainian troops through the winter months, also met Britain's new prime minister, Rishi Sunak, on Wednesday in London, where they discussed the Atlantic alliance's continued support for Ukrainian sovereignty.

Stoltenberg is the first international leader to visit Sunak at his Downing Street residence, and the meeting comes as Britain looks to update its Integrated Review of defence priorities as the government weighs public spending cuts.

Britain is a major contributor to the NATO alliance but public finances are under pressure.

The government will lay out spending cuts and tax rises in a budget on Nov. 17, putting in doubt a target to spend 3% of national output on defence by 2030. Wallace said he would continue to fight for defence budgets to modernise his forces.