France will stand by Ukraine's side, President Emmanuel Macron said in a televised address to his nation, adding that Russia's action against the eastern European country will have "durable and deep" consequences for the continent.

Russian forces invaded Ukraine by land, air and sea on Thursday in the biggest attack by one state against another in Europe since World War II.

Western countries fear a conflict on a scale unseen in Europe at least since the Yugoslav and Chechen wars of the 1990s, when hundreds of thousands died and millions fled.