The Group of Seven economic powers on Sunday warned Russia that a potential invasion of Ukraine would result in "massive" repercussions and severe economic suffering.

A joint statement by G-7 foreign ministers and the European Union's foreign affairs chief urged Russia to de-escalate its military build-up near the Ukrainian border, follow diplomatic channels, and respect its international commitments on transparency of military activities.

"Any use of force to change borders is strictly prohibited under international law. Russia should be in no doubt that further military aggression against Ukraine would have massive consequences and severe cost in response," said the statement.

Russia, on its part, has denied planning any attack but accuses Ukraine and the U.S. of destabilising behaviour, and argued it needs security guarantees for its own protection.

Russian President Putin has said talk of an invasion is "provocative" and accused Ukraine and the military alliance NATO of fanning tensions.