The Ukrainian president has said he had evidence that the Russian military tanks are massing along the border.
Petro Poroshenko has shown Sky News images of what he claims are tanks lining up along the border, close to where Russia stores its ammunition.
He said: “This is the tank base just 18km from our border, this was happening in September, October, and now.
“This is 18km from my border, this is the warehouse where they have their ammunition, we should be prepared to protect my country.
“If the whole world has no reason to trust Putin, Ukraine definitely doesn’t have a reason to go with him.”
He also used the interview to appeal for help from Western leaders.
His comments come amid rising tensions between the two former Soviet neighbours.
Russia seized three Ukrainian navy ships and their crew in the Kerch Strait after accusing them of venturing into their territory.
Russia is continuing to block the strait and refuses to free the Ukrainian sailors.
Ukraine rejects the charge that they were trespassing in Russian waters and said that two of its ports in the Azov Sea are effectively under blockade by Russia.
Moscow denies restricting any shipping.
Martial law has been imposed in some parts of Ukraine over the crisis.