The last time that Ursula von der Leyen travelled to Kyiv, in late February, she arrived in the midst of a gruelling winter. Ukraine was suffering widespread blackouts caused by Russian strikes. The population endured sub-zero temperatures without heating.

This week, on her second trip this year, she declared upon arriving at the train station: "The tide is turning."

It was a bold statement that captured a remarkable transformation in less than five months.

With the battle lines stuck in a war of attrition, Ukraine has moved the fighting to the skies, launching long-range drone strikes against Russia's oil refineries, some of them thousands of kilometres away from the contact line. The strategy has strained Moscow's war chest and forced the energy-rich country to restrict fuel exports.

"Russia may have darkened your skies with smoke. But no one is fooled. No cloud of smoke can hide the reality on the battlefield," von der Leyen said on Wednesday, standing next to Ukrainian President Volodymyr Zelenskyy.