VIENNA — Ukraine said on Thursday that Russia had massed 106,000 troops and 1,500 tanks near its border and called for “verified withdrawal” of Russian forces, while Moscow repeated warnings that it could “take all necessary measures” to assure its security, as a third round of talks on military security in Eastern Europe failed to yield a breakthrough.
Russian officials did not close the door on diplomacy, but sounded an increasingly pessimistic note. In Moscow, Sergei A. Ryabkov, a deputy foreign minister, said in a television interview that it was premature to convene more negotiations until the West abandoned what he called a “dead-end” approach. In Vienna, the United States reiterated it was prepared “for an open dialogue” but would “reject blackmail and never allow aggression and threats to be rewarded.”
The exchanges at an international meeting left tensions high and the implicit threat of further Russian military intervention in Ukraine on the table. Russia says the threat posed by Western military activity near its borders, particularly in Ukraine, has reached an unacceptable level and has demanded immediate “security guarantees” including NATO’s agreement to roll back its presence in the region.
Ukraine, participating for the first time in this week’s diplomacy, said Russia’s massing of troops needed to be reversed.
“The Russian leadership proves once again Moscow’s voluntarism to point the gun at our common European security at any moment they want,” said Ukraine’s representative, Yevhenii Tsymbaliuk.
Thursday’s talks were at a lower diplomatic level than the negotiations in Brussels and Geneva earlier this week, with no one above the ambassador rank in attendance from the key countries involved. They were being held at a regular meeting of the Organization for Security and Cooperation in Europe, a 57-country body that includes Russia, Ukraine and the United States, and is expected to serve as a key venue for more negotiations if the Kremlin decides to pursue its aims diplomatically.
“It seems that the risk of war in the O.S.C.E. area is now greater than ever before in the last 30 years,” Foreign Minister Zbigniew Rau of Poland said in opening the session. Poland took over the rotating chairmanship of the organization this year.
Despite representing Poland, one of Russia’s most vocal critics in Europe, Mr. Rau appeared to hold out an olive branch to the Kremlin even as he implicitly rebuked President Vladimir V. Putin for trying to re-establish a sphere of influence in the region.
“We are not indifferent to security objections voiced by participating states,” Mr. Rau said. “I believe that the O.S.C.E. is the right platform to discuss every aspect of comprehensive security.”
It was the latest sign that Western countries are scrambling to engage with Russia, which has warned of a “military-technical” response if concerns over its security — such as over Western military cooperation with Ukraine — are not addressed.
Understand the Escalating Tensions Over Ukraine
A brewing conflict. Antagonism between Ukraine and Russia has been simmering since 2014, when the Russian military crossed into Ukrainian territory, annexing Crimea and whipping up a rebellion in the east. A tenuous cease-fire was reached in 2015, but peace has been elusive.
A spike in hostilities. Russia has recently been building up forces near its border with Ukraine, and the Kremlin’s rhetoric toward its neighbor has hardened. Concern grew in late October, when Ukraine used an armed drone to attack a howitzer operated by Russian-backed separatists.
Ominous warnings. Russia called the strike a destabilizing act that violated the cease-fire agreement, raising fears of a new intervention in Ukraine that could draw the United States and Europe into a new phase of the conflict.
The Kremlin’s position. President Vladimir V. Putin of Russia, who has increasingly portrayed NATO’s eastward expansion as an existential threat to his country, said that Moscow’s military buildup was a response to Ukraine’s deepening partnership with the alliance.
A measured approach. President Biden has said he is seeking a stable relationship with Russia, though tension has been rising. So far, his administration is focusing on maintaining a dialogue with Moscow, while seeking to develop deterrence measures in concert with European countries.
While Russia denies it has plans to invade Ukraine, researchers have identified some new signs of Russian troops moving toward the Ukrainian border in recent days.
But it was far from clear whether Russia would be willing to proceed with diplomacy. Russian officials have said they would decide on next steps after this week’s talks. Russia’s foreign minister, Sergey V. Lavrov, said Moscow was awaiting a written response from the United States.
“The hard reality right now is that we were promised a written reaction,” Mr. Lavrov said in an interview aired on Thursday, according to the Interfax news agency. “We will wait for it. And then we will determine our next steps.”
Russia’s representative at the talks on Thursday in Vienna, Aleksandr Lukashevich, underscored that while Moscow was not ruling out the possibility of further negotiations, it was prepared to make such a determination in the coming weeks. Military analysts have noted that were Russia to invade Ukraine, the wintertime frozen ground would be advantageous to its heavy armor.
“If we do not hear a constructive response on our proposals in a reasonable time frame,” Mr. Lukashevich said in remarks released by his office, “we will be forced to draw the corresponding conclusions and take all necessary measures to assure the strategic balance and removing unacceptable threats to our national security.”