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 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.

On Wednesday, the Kremlin condemned comments by outgoing NATO chief Jens Stoltenberg as “dangerous”, Reuters reports. Stoltenberg had suggested that allowing Ukraine to use Western long-range missiles to strike Russian territory would not trigger an escalation from Moscow.