MOSCOW — President Vladimir V. Putin of Russia demanded “legal guarantees” on Wednesday that the NATO alliance would never expand eastward, ratcheting up the stakes as the West scrambled to respond to Russia’s military buildup near Ukraine.
Mr. Putin, who has increasingly portrayed Ukraine’s deepening military partnership with the United States and other NATO countries as an existential threat, said that Moscow wanted to start talks with the West to reach an agreement that would block the alliance’s expansion. Left unsaid was what Western officials describe as a growing threat of military action by tens of thousands of Russian troops massing close to the border with Ukraine — a former Soviet nation that seeks to join the Western alliance.
“The threat on our western borders is, indeed, rising, as we have said multiple times,” Mr. Putin said at a ceremony for ambassadors at the Kremlin on Wednesday. “In our dialogue with the United States and its allies, we will insist on developing concrete agreements prohibiting any further westward expansion of NATO and the placement there of weapons systems in the immediate vicinity of Russian territory.”
Mr. Putin’s demand is a nonstarter for NATO, whose officials say they are committed to allowing every country to pick its alliances for itself. Foreign ministers from NATO member countries gathered Wednesday in Latvia, a former Soviet republic bordering Russia, in a signal of the alliance’s cohesion and its support for its ex-Soviet member states.
“It’s only Ukraine and 30 NATO allies that decide when Ukraine is ready to join NATO,” Jens Stoltenberg, the secretary general of the alliance, told reporters in Riga, the Latvian capital. “Russia has no veto, Russia has no say, and Russia has no right to establish a sphere of influence trying to control its neighbors.”
But Mr. Putin appears to be pushing for direct talks with President Biden, who has sought dialogue with the Kremlin and a “stable and predictable” relationship with Russia, seeking out agreement on issues of mutual interest. Russian officials have said they are preparing for a call or videoconference between the two presidents as early as this month, and Secretary of State Antony J. Blinken is set to meet with his Russian counterpart, Sergey V. Lavrov, in Stockholm on Thursday.
“We don’t know whether President Putin has made the decision to invade,” Mr. Blinken said in Riga. “We do know that he is putting in place the capacity to do so on short order.”
In his speech on Wednesday, Mr. Putin denied that Russia was threatening Ukraine. Rather, he said, Russia was simply taking “adequate military and technical measures” to respond to growing NATO activity in and around Ukraine, near Russian borders. A day earlier, he warned that if missiles were deployed in Ukraine that could reach Moscow within minutes, Russia would respond in kind.
“Just look at how close to Russian borders the military infrastructure of the North Atlantic alliance has come,” Mr. Putin said Wednesday. “For us, this is more than serious.”
The United States provides Ukrainian forces with training and antitank weaponry in Ukraine’s fight against Russian-backed separatists in the country’s east. Six thousand Ukrainian and NATO troops held joint exercises in September. Mr. Putin has expressed particular irritation at NATO activity in the Black Sea region, including what he said were approaches as close as 12 miles to Russian borders by Western nuclear-capable bombers.
“NATO is not a threat to anyone,” Mr. Stoltenberg, the alliance’s secretary general, said, rejecting the idea that Russia had reason to worry about those activities. “This idea that NATO support to a sovereign nation is a provocation is just wrong.”
American officials say that Russia has been moving the estimated 90,000 troops it has near its border with Ukraine in ways that might presage an invasion, and it has been sharing intelligence with its allies. Western officials have said that they do not believe that Mr. Putin has made a decision about whether to invade Ukraine, and that there is a window to try to enhance deterrence and affect his judgment.
It is not yet clear what such deterrence would look like, since Ukraine is not a NATO member. But Western officials said Wednesday that they were prepared to impose economic sanctions that would be more painful than those that came after Russia’s annexation of Crimea in 2014. William J. Burns, the C.I.A. director, relayed that message to the Kremlin when he visited Moscow last month, Mr. Blinken said.
“We’ve made it clear to the Kremlin that we will respond resolutely, including with a range of high-impact economic measures that we’ve refrained from using in the past,” Mr. Blinken said.
Steven Erlanger contributed reporting from Vienna.