Moscow has warned the US it should take Russia's nuclear warnings seriously to avoid World War Three.
Dmitry Medvedev, deputy chairman of Russia's security council and who served as the country's president from 2008 to 2012, warned the US on Saturday it was "wrong" to believe "that the Russians will never cross a certain line".
He told Russian-state broadcaster RT that Moscow believed the current US and European political establishments lacked the "foresight and subtlety of mind" displayed by the late Henry Kissinger.
"If we are talking about the existence of our state, as the president of our country has repeatedly said, your humble
servant has said, others have said, of course, we simply will not have any choice," Mr Medvedev said.
Russia has been signalling for weeks to the West that Moscow will respond if the US and its allies help Ukraine fire longer-range missiles deep into Russia.
US diplomats have previously said Washington is not seeking to escalate the war in Ukraine.
It's not the first time Mr Medvedev has warned of a serious escalation of the Ukraine conflict.
Back in September, he threatened that Ukraine's incursion into the Russian territory of Kursk had given Russia formal grounds to use nuclear weapons.
?Listen to The World With Richard Engel And Yalda Hakim on your podcast app?
It comes as Ukraine's capital of Kyiv became the subject of an overnight aerial attack which lasted until midday today and saw one person injured, city officials said. All drones had been shot down.
Read more from Sky News:
Queen Elizabeth II will appear in Paddington 3
Combative past of new Tory leader
President Volodymyr Zelenskyy, who has recently seen North Korean troops join the fight alongside Russia's army, said strikes were also reported in the central Poltava and northeastern Sumy and Kharkiv regions.
"This year, we have faced the threat of 'Shahed' drones almost every night - sometimes in the morning, and even during
the day," he wrote on social media, referring to the Iranian-made attack drones used by Russia.
Kyiv's military said on Friday that Moscow's forces had launched more than 2,000 drones at civilian and military targets
across Ukraine in October alone.
Russia has denied aiming at civilians and said power facilities are legitimate targets when they are part of Ukrainian military infrastructure.
(c) Sky News 2024: Dmitry Medvedev warns US it should take Russia nuclear warnings seriously to avoid World Wa
Police investigating historical sex offence allegations against Russell Brand understood to have handed file to CPS
'Where are they?': Flood-hit Spanish towns desperate for leadership
Girl, 10, dies after being bitten by family dog at home in North Yorkshire
Kemi Badenoch wins race to be next Tory leader
Kemi Badenoch's husband Hamish has one thing in common with Denis Thatcher - but seems more like Philip May