Ukraine's barrage of major long-range drone strikes on Russia show that the war is increasingly swinging in Kyiv's favour, an expert has revealed.It comes as a wave of almost 600 Ukrainian drones attacked Russia overnight killing four people, authorities said on Sunday, as Ukrainian President Volodymyr Zelensky called the barrage an 'entirely justified' retribution for Moscow's own pummelling of Ukraine.Russia's defence ministry reported that air defences shot down 556 drones across the country overnight, followed by another 30 after dawn.Stretching up to 700 miles from the Ukrainian border, the barrage stands as one of the largest Ukrainian strikes of the war to date, taking out a navy vessel and drones. In recent weeks, Ukraine has stepped up its drone strikes on Russian territory as it increasingly relies on its own domestic weapons manufacturing.Keir Giles, a Russia analyst at Chatham House, noted that this shift demonstrates Ukraine gradually gaining the strategic upper hand, as Putin will have to accept his country is facing defeat.Speaking to the Daily Mail he said: 'The drone strikes on Russia will not win the war on their own, but they are one indication among many at the moment that the advantage in the war is swinging back Ukraine's way.''Ukraine is exploiting the fact that Russia is a big place, and it is not possible to defend everything within Russia in a meaningful manner. 'Even if Russia were to dedicate as much effort and resources to air defence as Ukraine has been forced to do under the relentless Russian bombardment, they would still not be able to protect all of the vital facilities that Ukraine is now targeting.'