MOSCOW: President Vladimir Putin said on Sunday that Russia’s defence ministry was working on different ways to respond if the United States and its NATO allies help Ukraine to strike deep into Russia with long-range Western missiles.

The 2-1/2-year-old Ukraine war has triggered the biggest confrontation between Russia and the West since the depths of the Cold War, and Russian officials say the war is now entering its most dangerous phase.

Russia has been signalling to the United States and its allies for weeks that if they give permission to Ukraine to strike deep into Russian territory with Western-supplied missiles, then Moscow will consider it a major escalation.

Putin said on Sept. 12 that Western approval for such a step would mean “the direct involvement of NATO countries, the United States and European countries in the war in Ukraine” because NATO military infrastructure and personnel would have to be involved in the targeting and firing of the missiles.

Putin said that it was too early to say exactly how Russia would react to such a move but that Moscow would have to respond accordingly and different options were being examined.

“(The Russian defence ministry) is thinking about how to respond to the possible long-range strikes on Russian territory, it will offer a range of responses,” Putin told Russian state TV’s top Kremlin reporter, Pavel Zarubin.

With Russia advancing at the fastest rate in eastern Ukraine since the first months of the invasion, Ukrainian President Volodymyr Zelenskiy has been pleading with the West to allow Kyiv to fire deep into Russia with Western missiles.

The United States has not said publicly if it will allow Ukraine to strike Russia, but some US officials are deeply sceptical that doing so would make a significant difference in the war.

Ukrainian forces already strike deep into Russia on a regular basis with long-range drones.