Ukrainian officials are reporting that blasts have been heard in the capital of Kyiv this morning.
It follows satellite images earlier showing a convoy of Russian military vehicles three miles wide outside the city.
Meanwhile, Vladimir Putin's ordered Russian nuclear forces to be put on high alert in response to, what he calls, "aggressive statements" by NATO nations.
The White House has condemned the dramatic escalation following a raft of economic sanctions on Moscow.
President Joe Biden is to host a call with Western leaders later today.
Asami Terajima is a journalist in Kyiv - she says the way those in the country are handling the situation should be praised.
"Obviously people are worried but they are still calm in that they are not panicking.
"They're not going to supermarkets and trying to buy all the products and stuff.
"They're just following what the government says, staying at home when there's a siren or, or going to the shelter and doing whatever that's needed to stay safe."
