Dan Rivers reports from inside Ukraine's icy northern border, on the country's defences against any possible Russian ground attack
Amid warnings of a potential attack in February, Ukraine's people have told ITV News they are ready for attack
Russia has upward of one million people in the Armed Forces, more than four times Ukraine's force strength.
But Lieutenant Alexandra Stupak, from the Ukranian Frontier Force, told ITV News: "We have special units that react to any event. For example if there is any provocation then this reserve force will reinforce our units here in the quickest possible time".
Some Ukrainian citizens are preparing for the worst scenario by conducting army and first aid training. They too are ready.
Igor Beletzy teaches tactics and first aid - his classroom is full of weapons locals may have to use in anger.
Mr Beletzy is prepared for all outcomes: "Let Putin stop the shedding of blood from our side and their side. We can be good neighbours. But if he finally comes to us, we will meet him with force."
A local army commander was blunt about the fate awaiting, he said: "They will get a warm reception, with plenty of coffins."
ITV News Correspondent Dan Rivers on the forces in the two countries
US President Joe Biden spoke to his Ukrainian counterpart Volodmyr Zelenskyy on Thursday, warning Russia could invade within the next 30 days.
The White House said President Biden warned there is a “distinct possibility” Russia could take military action against Ukraine in February.
“Had a long phone conversation with POTUS,” Zelenskyy tweeted. “Discussed recent diplomatic efforts on de-escalation and agreed on joint actions for the future.
"Thanked President Joe Biden for the ongoing military assistance. Possibilities for financial support to Ukraine were also discussed.”
The White House said in a statement that Biden told Zelenskyy he was “exploring additional macroeconomic support to help Ukraine’s economy” as it comes under pressure as a result of Russia’s military buildup.
The US president reiterated American and allied support, including recent deliveries of US military aid.
Kremlin spokesman Dmitry Peskov told reporters earlier that the response from the U.S., and a similar one from NATO, left “little ground for optimism.”
Foreign Minister Sergey Lavrov said the U.S. response contained some elements that could lead to “the start of a serious talk on secondary issues,” but emphasised that “the document contains no positive response on the main issue.”
Mr Lavrov said top officials will submit proposals to President Putin and Mr Peskov said the Russian reaction would come soon.
The official comments reflect that it is Putin who will single-handedly determine Russia’s next moves.
He has warned of unspecified “military-technical measures” if the West refuses to heed the demands.
Mr Peskov added that President Putin and President Biden will decide whether they need to have another conversation following two calls last month.