A Ukrainian journalist who fled over border said: “Nato is not willing to defend because Nato is afraid of World War Three, but it’s already started and it’s Ukrainian children who are there taking the hit.”
Vladimir Putin has said its strategic nuclear weapons forces are on high alert, prompting fears over what could happen next.
Fifa is set to ban Russia's national teams from international football until further notice, reports suggest.
"To the people of Britain, I ask you that when you come home from work today, hug your family, hug your kids, close your eyes and for a second just imagine there are explosions outside your house."
Putin said he was responding to "aggressive statements regarding our country" from Nato members.
The US has also joined the EU in agreeing to freeze assets of Vladimir Putin and Sergeĭ Lavrov.
He also admitted that Russia did influence UK votes.
"What was done on Monday was weak, really weak," said Tom Tugendhat, the chairman of the Foreign Affairs Committee.
“Those standing with puffed chests about ‘getting Brexit done’ have yet to say or show how the UK might benefit."