The announcement of a partial mobilization by Russian President Vladimir Putin only shows the "catastrophic failure" of the invasion and strengthens the conviction of the western allies to support Kyiv, Truss said on her first trip abroad as head of government. New arms from the UK would be arriving in Ukraine "at this very moment," Truss noted.

The conservative party leader also announced that by 2030 London would spend three percent of its gross domestic product (GDP) on defense - significantly more than the two percent required by NATO.

In her speech, Truss also called for economic unity as a powerful tool against aggression. The G7 and its like-minded partners should "act as economic NATO" and together "defend our prosperity," she said.