"If something like this happens, Russia will give a tough response using more powerful weapons," warned a prominent Russian lawmaker.

A close ally of President Vladimir Putin warned Western governments on Thursday that a nuclear war would ensue if they gave the green light for Ukraine to use long-range Western weapons to strike targets deep inside Russia.

Russian officials delivered dissonant statements in the past week about how Moscow would respond to Western weapons striking deep inside its territory, and whether such attacks will happen at all. Russian diplomats played on the now-familiar threat of a nuclear response.