UK Prime Minister Andy Burnham has said London will continue "to support Ukraine 100%", after Moscow warned of "consequences" following confirmation that British-made drones were used in recent Ukrainian strikes in Russia.
"We are not fair-weather friends, we will be there in Ukraine's hour of need and that won't change," he said.
The Russian embassy in the UK earlier accused Britain of "deliberately opting for an escalation of the Ukraine crisis", saying "the deeper its involvement in the conflict... the higher the price it will pay".
Kyiv has stepped up long-range attacks on Moscow and other Russian regions, targeting oil refineries and warehouses of the largest online retailer Wildberries.
Asked on Tuesday about the Russian threat, Burnham maintained that the UK was "providing support so that Ukraine can defend itself and that's been the British position all the way through this conflict, by previous prime ministers - it remains the case with me".