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.

The Kremlin has had little success invoking its nuclear arsenal to deter Ukraine and the West from using new tactics to stop Russia’s invasion. That may be changing.

Russian President Vladimir Putin has warned NATO alliance leaders that a move to lift restrictions on Ukraine’s use of longer-range Western missiles to strike deep inside his country would be considered an act of war.