BRUSSELS xe2x80x94 After four hours of talks with Russia, NATO leaders said that they were willing to engage in serious diplomacy with Moscow over arms control and missile deployments in Europe, but they rejected outright Russian demands that the alliance stop enlargement, pull back its forces from member states bordering Russia and guarantee that Ukraine will never join.

xe2x80x9cSignificant differencesxe2x80x9d remained between NATO and Russia, and xe2x80x9cour differences will not be easy to bridge,xe2x80x9d said the NATO secretary-general, Jens Stoltenberg, after the meeting.

xe2x80x9cThere is a real risk for new armed conflict in Europe,xe2x80x9d Mr. Stoltenberg said, one that would carry severe economic and other costs to Moscow, he added, and would bring about new military deployments in member states near Russia.

The United States and its NATO and European Union allies are pressing Russiaxe2x80x99s president, Vladimir V. Putin, to abandon any further invasion of Ukraine, pull back his troops and engage in reciprocal diplomacy on Russiaxe2x80x99s security concerns xe2x80x94 and NATOxe2x80x99s.

Mr. Stoltenberg said that NATO allies urged Russia to xe2x80x9cimmediately de-escalate the situation in Ukraine,xe2x80x9d where close to 100,000 Russian troops have massed near the borders, and to respect the sovereignty and territorial integrity of its neighbors. Russian representatives did not commit to pulling back the troops, nor did they reject the demand, officials said.

NATO allies reaffirmed their refusal to accept Russian demands to stop further enlargement with countries that wished to join the alliance and to withdraw all allied troops from NATO members bordering Russia. Those demands were repeated after the talks by the Russian deputy foreign minister, Aleksandr V. Grushko, a former permanent representative to NATO from 2012-18.

xe2x80x9cThis is a principled position, and we will not move from it,xe2x80x9d he said. But he called the meeting xe2x80x9crather honest, direct, deep and comprehensive,xe2x80x9d adding: xe2x80x9cBut at the same time, it showed a great amount of divergence on fundamental questions.xe2x80x9d

xe2x80x9cThis was a heart-to-heart discussion,xe2x80x9d Mr. Grushko said. xe2x80x9cI think we were able to communicate to the members of the alliance that the situation is becoming unbearable.xe2x80x9d It was a chance to remind NATO that Russia, too, may have a say in the future of European security, which could xe2x80x9ccarry risks,xe2x80x9d Mr. Grushko said. xe2x80x9cWe support peaceful solutions based on balance,xe2x80x9d he said.

Mr. Grushkoxe2x80x99s comments indicated that Russia, for now, was not closing the door to further diplomacy, even though it has not committed to talks beyond this week. Russian officials said earlier this week that they would wait until the end of a full week of talks xe2x80x94 which began with an informal dinner in Geneva on Sunday and will wrap up on Thursday in Vienna xe2x80x94 before making a decision on how to continue.

Russian officials deny that the country is planning to invade Ukraine, but Mr. Putin has warned of an unspecified xe2x80x9cmilitary-technicalxe2x80x9d response if the West does not agree to Russiaxe2x80x99s demands. Mr. Grushko reiterated that warning, without adding clarity to it.

xe2x80x9cIf NATO moves on to a policy of containment, then there will be a policy of counter-containment from our side,xe2x80x9d Mr. Grushko said. xe2x80x9cIf there is deterrence, there will be counter-deterrence.xe2x80x9d

Wendy R. Sherman, the deputy secretary of state who led the U.S. delegation to the talks, called some of Russiaxe2x80x99s demands xe2x80x9csimply non-startersxe2x80x9d and emphasized NATOxe2x80x99s offers to Moscow for diplomacy.

Briefing reporters in Brussels, Ms. Sherman said that NATO officials laid out for the Russians areas xe2x80x9cwhere we can work together and make real progress,xe2x80x9d including on arms control, missile deployments, risk reduction and greater transparency in military exercises.

Mr. Stoltenberg said that NATO allies offered Russia a series of further meetings on wider issues of European security, including the issues Ms. Sherman raised. But while the Russian delegation was generally positive, he said, they would not or could not commit to a new meeting. That is another indication that even Russiaxe2x80x99s top diplomats may not know what Mr. Putinxe2x80x99s intentions really are.

Ms. Sherman said that she hoped that after this long week of discussions with top Russian representatives, which continues on Thursday in Vienna, that they xe2x80x9cwill return to Moscow and that they will brief the president of Russia, and that they will all appreciate and understand, and the president of Russia will agree, that diplomacy is the correct path.xe2x80x9d

She said the decision was up to Mr. Putin. xe2x80x9cIf Russia walks away,xe2x80x9d she said, it would be xe2x80x9cquite apparent that they were never serious about pursuing diplomacy at all.xe2x80x9d

Washington and its allies promise xe2x80x9csevere costs and consequencesxe2x80x9d if Russia further invades Ukraine, imposing xe2x80x9ca severe price on Russiaxe2x80x99s economy and financial system,xe2x80x9d Ms. Sherman said.

Moscowxe2x80x99s choice will be important for the fate of the Nord Stream 2 pipeline, meant to transport natural gas from Russia to Germany in the future, Ms. Sherman repeated. xe2x80x9cFrom our perspective, itxe2x80x99s very hard to see gas flowing through the pipeline or for it to become operational if Russia renews its aggression on Ukraine.xe2x80x9d

The pipeline, which is not yet operational, is a Russian geopolitical project that undermines the security of a xe2x80x9csignificant part of the Euro-Atlantic community,xe2x80x9d she said.

The meeting at NATOxe2x80x99s Brussels headquarters was the second stop in a diplomatic roadshow focused on the Kremlin, after talks in Geneva on Monday between Russian and American officials. The meeting on Thursday in Vienna with the 57-member Organization for Security and Cooperation in Europe, including Ukraine, will take place at a lower diplomatic level xe2x80x94 with ambassadors rather than foreign ministers and other top officials.

If Russia decides to pursue its aims diplomatically rather than go to war again in Ukraine, some of the negotiations on future European security will take place under the auspices of the O.S.C.E.

The Russian delegation at NATO was led by Mr. Grushko and the deputy defense minister, Aleksandr V. Fomin. They spoke at length at the start of the meeting, laying out Russiaxe2x80x99s demands and concerns. In the subsequent exchanges, all 30 NATO members spoke with what Ms. Sherman called xe2x80x9camazing unityxe2x80x9d on NATOxe2x80x99s core values, which include its openness to any country that wishes to join and qualifies to do so.

Before Wednesdayxe2x80x99s meeting, Mr. Grushko told reporters that xe2x80x9cthe moment of truth in our relationship with the alliance is arriving,xe2x80x9d according to Russian news agencies.

xe2x80x9cThis wasnxe2x80x99t an easy discussion, but that is exactly why this meeting was so important,xe2x80x9d Mr. Stoltenberg said, adding that NATO allies and Russia had xe2x80x9ca very serious and direct exchange on the situation in and around Ukraine, and implications for European security.xe2x80x9d

The United States and its NATO allies hope that Mr. Putin will decide to negotiate, as he is now confronted with threats of punishing economic sanctions and new deployments in NATO allies bordering Russia, like Poland and the Baltic countries.

The issue of new deployments is a live discussion, the Estonian prime minister, Kaja Kallas, told Reuters. xe2x80x9cOf course, we are discussing with our allies to increase their presence here to act as a deterrent,xe2x80x9d she said. xe2x80x9cIf you look at the map, the Baltic states are a NATO peninsula and therefore we have our worries.xe2x80x9d

Polish officials also seemed pleased with the American and NATO responses to Moscowxe2x80x99s demands. xe2x80x9cOur position is clear,xe2x80x9d Lukasz Jasina, the spokesman for Polandxe2x80x99s foreign minister, said. xe2x80x9cOnly NATO and member countries decide about NATO matters. And no one else.xe2x80x9d

Russia is a neighbor but cannot be allowed to pressure others, said Polandxe2x80x99s deputy foreign minister, Marcin Przydacz. xe2x80x9cWhat Russia has left is intimidation, but as this smaller partner, with a diminishing role in the world, the argument that xe2x80x98if you do not listen to us, we will beat the smaller colleaguexe2x80x99 cannot be taken into account.xe2x80x9d

After Mondayxe2x80x99s talks, Sergei A. Ryabkov, who led the Russian side, warned that if the West did not agree to Russiaxe2x80x99s demands to pull back NATOxe2x80x99s footprint in Eastern Europe and reject any future membership for Ukraine, it would face unspecified consequences that would put the xe2x80x9csecurity of the whole European continentxe2x80x9d at risk.

The Americans and Russians say that after this week, they will discuss whether to keep talking.

That is, unless Mr. Putin decides to argue that Washington and its allies do not take Russiaxe2x80x99s demands seriously xe2x80x94 and chooses to use this week as a pretext to go to war.

Anton Troianovski reported from Bratislava. Reporting was contributed by Monika Pronczuk in Brussels and Michael Crowley in Washington.