NATO Secretary General Jens Stoltenberg on Friday ruled out any halt to the continued expansion of the military organization to address Russian security concerns, rejecting a key part of President Vladimir Putin’s demands for easing tensions with Ukraine.

“We will not compromise on core principles, including the right for every nation to decide its own path, including what kind of security arrangements it wants to be a part of,” Stoltenberg told reporters in Brussels after an extraordinary meeting of NATO foreign ministers.

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U.S. Secretary of State Antony Blinken and his counterparts held online talks to prepare for the first meeting of the NATO-Russia Council in more than two years. The meeting, set for Wednesday in Brussels, will give NATO ambassadors the chance to discuss Putin’s security proposals with Russia’s envoy face to face.

Much contained in the documents that Moscow has made public — a draft agreement with NATO countries and the offer of a treaty between Russia and the United States — appears to be a non-starter at the 30-country military organization, despite fears that Putin might order an invasion of Ukraine.

NATO would have to agree to halt all membership plans, not just with Ukraine, and to end military exercises close to Russia’s borders. In exchange, Russia would respect the international commitments it’s signed up to on limiting wargames, as well as end aircraft buzzing incidents and other low-level hostilities.

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Endorsing such an agreement would require NATO to reject a key part of its founding treaty. Under Article 10 of the 1949 Washington Treaty, the organization can invite in any willing European country that can contribute to security in the North Atlantic area, as well as fulfill the obligations of membership.

Stoltenberg said the Russian military buildup that sparked the invasion worries has continued.

“We see armored units, we see artillery, we see combat-ready troops, we see electronic warfare equipment and we see a lot of different military capabilities,” he said.

This buildup, combined with Russia’s security demands, and its track record in Ukraine and Georgia, “sends a message that there is a real risk for a new armed conflict in Europe,” Stoltenberg said.

Russia annexed Ukraine’s Crimean Peninsula in 2014 and later backed a separatist rebellion in the country’s east. Over more than seven years, the fighting has killed over 14,000 people and devastated Ukraine’s industrial heartland, known as Donbas.

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Russia denies that it has fresh plans to attack its neighbor, but Putin wants legal guarantees that would rule out NATO expansion and weapons deployments. Moscow says it expects answers to its security proposals this month.

Despite the rhetoric, Ukraine simply cannot join NATO with Crimea occupied and fighting in the Donbas because the alliance’s collective security guarantee — that an attack on one ally is considered to be an attack on them all — would draw it into war if the country became a member.

Indeed, NATO’s help in the event of an invasion is unlikely to involve major military muscle.

“Ukraine is a very close partner,” Stoltenberg said. “We provide support to Ukraine. But Ukraine is not covered by NATO’s collective defense clause because Ukraine is not a NATO member.”

Stoltenberg did say that NATO is willing to discuss arms control with Moscow, but that Putin cannot be permitted to impose restrictions on how the organization protects member countries close to Russia’s borders like Estonia, Latvia, Lithuania and Poland.

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“We cannot end up in a situation where we have a kind of second-class NATO members; where NATO as an alliance is not allowed to protect them in the same way as we protect other allies,” he said.

Friday’s meeting was the first in a flurry of high-level talks involving NATO, senior U.S. and Russian officials and the Organization for Security and Cooperation in Europe over the next week.

French President Emmanuel Macron said Friday that it’s important to speak with Russia about its concerns, and that he will talk again with Putin “in the coming days.”

“Dialogue does not mean giving in,” Macron told reporters in Paris at an event to mark the start of France’s six-month term at the helm of the European Union.

The NATO-Russia Council was set up two decades ago. But NATO ended practical cooperation with Russia through the NRC in 2014 after it annexed Crimea. Wednesday’s meeting will be the first since July 2019. NATO officials say Russia has refused to take part in meetings as long as Ukraine was on the agenda.