Ukrainian troops have advanced up to 30 km into Russia in possibly the most serious border incursion of the conflict. Ukraine's forces stormed into Russia's southwestern Kursk region, deploying around 1,000 troops and more than two dozen armoured vehicles and tanks, according to the Russian army. Russia's top general vowed on Wednesday to crush the incursion and push the Ukrainian fighters back to the border. NDTV's Vishnu Som explains the latest developments in the major Ukrainian offensive inside Russian territory.