G7 finance ministers have warned Russia of "massive" economic consequences if it decides to invade Ukraine, to which they have also pledged swift and decisive support.

"The ongoing Russian military build-up at Ukraine's borders is a cause for grave concern. We, the G7 Finance Ministers, underline our readiness to act swiftly and decisively to support the Ukrainian economy," they wrote in a joint statement on Monday.

"Any further military aggression by Russia against Ukraine will be met with a swift, coordinated and forceful response," they added.

"We are prepared to collectively impose economic and financial sanctions which will have massive and immediate consequences on the Russian economy."