Dramatic moment Ukraine destroys key Russian bridge in Kursk delivering yet ANOTHER huge blow to Putin
Why has the Ukrainian invasion of Russia been so successful?
A DARING Ukrainian military push into Russia's Kursk region has become the largest attack on the country since World War Two.
Kyiv's forces have seized scores of villages, taken hundreds of prisoners and forced the evacuation of tens of thousands of civilians.
After more than a week of fighting, Russian troops are still struggling to drive out the invaders.
Why has Russian military been caught so unprepared?
- A long undefended border
Russia's regions of Kursk, Bryansk and Belgorod share a 720-mile border with Ukraine - including a 152-mile section in the Kursk region.
And it only had symbolic protection before Moscow invaded Ukraine in 2022.
It's been reinforced since then with checkpoints on key roads and field fortifications in places - but not enough to repel a Ukrainian assault.
The most capable Russian units are fighting in eastern Ukraine, leaving the border vulnerable to attack.
- Element of surprise
Ukrainian troops participating in the incursion were reportedly only told about their mission a day before it began.
The secrecy contrasted with last year's counteroffensive - when Ukraine openly declared its goal of cutting the land corridor to annexed Crimea.
Ukraine ended up failing as troops trudged through Russian minefields and were pummelled by artillery and drones.
But in Kursk, Ukrainian troops didn't face any of these obstacles.
Battle-hardened units easily overwhelmed Russian border guards and small infantry units made up of inexperienced conscripts.
The Ukrainians drove deep into the region in several directions - facing little resistance and sowing chaos and panic.
- Russia's slow response
The Russian military command initially relied on warplanes and choppers to try to stop the onslaught.
At least one Russian helicopter gunship was shot down and another was damaged.
Moscow began pulling in reinforcements, managing to slow Ukraine's advances - but failed to completely block troops.