President Vladimir V. Putin of Russia warned the United States and its Western allies on Thursday that should they permit Ukraine to fire weapons deeper into Russia, they would put his country “at war” with NATO.

Mr. Putin’s comments to a state television reporter came just a day before Prime Minister Keir Starmer of Britain was set to meet President Biden in Washington to discuss the prospect of lifting restrictions on Kyiv’s use of Western-supplied long-range weapons in its war with Russia.

In 30 months of war, Ukraine’s Western backers have made a series of concessions to Kyiv’s war effort, supplying Ukraine with increasingly powerful weapons including tanks, fighter jets and long-range missiles. Despite previous threats, Mr. Putin has yet to bring his war past Ukraine’s borders. But in his comments on Thursday — some of his most direct yet about the prospect of war with NATO — Mr. Putin said the West would have to supply not just hardware to Ukraine but also intelligence and technology, changing the West’s involvement and the prospects for a Russian response.

Here is what Mr. Putin said on Thursday:

Russian state media: Over the past few days, we have been hearing statements at a very high level in the United Kingdom and the United States that the Kyiv regime will be allowed to strike targets deep inside Russia using Western long-range weapons. Apparently, this decision is either about to be made, or has already been made, as far as we can see. This is actually quite extraordinary. Could you comment on what is going on?

President Putin: What we are seeing is an attempt to substitute notions. Because this is not a question of whether the Kyiv regime is allowed or not allowed to strike targets on Russian territory. It is already carrying out strikes using unmanned aerial vehicles and other means. But using Western-made long-range precision weapons is a completely different story.