Russia says the use of US long-range missiles by Ukraine will lead to "an appropriate and tangible" response. Such an attack inside Russian territory "would represent the direct involvement of the United States and its satellites in hostilities against Russia", a foreign ministry statement said.

The Kremlin warns Kyiv's use of such missiles would mark an escalation in the conflict, hours after Joe Biden gives the green light.

The U.S. decision to authorise long-range Ukrainian strikes could help Kyiv defend the foothold in Russia's Kursk region that it seized as leverage in any war talks, but may come too late to change the course of the war,