"We have not gone mad, we are aware of what nuclear weapons are," he said, adding: "We aren't about to run around the world brandishing this weapon like a razor."However, he said the results had already been "significant" - for example, the new territories Russia has illegally claimed after sham-referendums in four regions of Ukraine.He boasted that the annexations had made the Sea of Azov - which is bordered by south-east Ukraine and south-west Russia - an "internal sea" of Russia, adding that this was an aspiration of Russian Tsar Peter the Great.Last month, Russian forces were forced to retreat from Kherson city, the only regional capital they had seized since the February invasion.The setbacks on the frontline have led to Russia targeting Ukraine's power grid by launching massive air strikes across the country,The airstrikes have caused widespread damage to Ukraine's energy infrastructure, leaving millions without heating and electricity for hours, or even days, as temperatures dropped below zero."