She will tell a recovery conference in Switzerland on Monday that the UK will “do everything possible to ensure Ukraine wins the war and recovers”.
Ukrainian President Volodymyr Zelensky has asked the UK to champion the recovery of the capital of Kyiv and the surrounding region, according to the Foreign Office.
But attempts to recover and rebuild are made more challenging by the Russian President’s ability to strike the capital with missiles as his forces make creeping advances in the east.
The city of Lysychansk has fallen to Russian forces as Ukraine’s military command confirmed that its troops have been forced to withdraw. It had been Ukraine’s last bastion in the eastern province of Luhansk and the subject of fierce fighting in recent days.
“The continuation of the defence of the city would lead to fatal consequences.
“In order to preserve the lives of Ukrainian defenders, a decision was made to withdraw,” Ukraine’s military said on Sunday.
Truss will use the conference in the city of Lugano to set out a vision to give immediate support and long-term commitments to work alongside the Ukrainians to shore up their defence of the country.
“Ukraine’s recovery from Russia’s war of aggression will be a symbol of the power of democracy over autocracy. It will show Putin that his attempts to destroy Ukraine have only produced a stronger, more prosperous and more united nation,” she is expected to say.
“The UK is resolute in its support of Ukraine’s territorial integrity and will remain at Ukraine’s side as it emerges as a strong, thriving and cutting-edge democracy.
“We have led on support for Ukraine during the war and will continue to lead in supporting the Ukrainian government’s reconstruction and development plan.”
Ms Truss will announce plans to host next year’s recovery conference as the Government commits to a Marshall Plan-style programme, echoing the one used to rebuild Europe after the Second World War.
“The UK will do everything possible to ensure Ukraine wins the war and recovers. We need to be in this for the long haul,” she is expected to add.
The Russian President has focused his assault on the eastern regions of Luhansk and Donetsk after withdrawing from the offensive in Kyiv as his troops faced fierce resistance.
Moscow claims that Russian forces have taken control of Lysychansk, the last major Ukrainian-held city in Luhansk.
Russia hit Kyiv with missile strikes last week in what Ukrainians called an intimidation attempt as they seek a return to normal life while still under siege.
Authorities said at least 19 people including two children were killed in a separate missile attack on the Kremenchuk in the town of Serhiivka near Odesa on Friday.
A further 19 were killed and 62 injured in a missile strike on a shopping centre in the central city of Kremenchuk on Monday, Ukrainian authorities said.