Russian Foreign Minister Sergey Lavrov on Thursday accused the U.S. and NATO of risking a “nightmare scenario of military confrontation” in Europe, warning the alliance against expanding military infrastructure in Ukraine.

“The alliance’s military infrastructure is being irresponsibly brought closer to Russia’s borders in Romania and Poland, deploying an anti-missile defence system that can be used as a strike complex,” Lavrov said in remarks at a conference of the Organisation for Security and Co-operation in Europe (OSCE), per BBC News.

The top Russian diplomat’s comments came amid fears that Moscow is planning an invasion of Ukraine. Tens of thousands of Russian troops have gathered along Ukraine’s border.

Since Russia’s unilateral annexation of Crimea in 2014, Ukraine has emerged as a major geopolitical dividing line between the West and Russia. That same year, a war began between Kremlin-backed rebels and Ukrainian troops in the eastern Donbass region. The conflict, which Russia claims it’s not involved in, has killed over 13,000 people.

Ukraine is not a full NATO member, but has sought to join the alliance for years and maintains a robust partnership with it. Members of the security alliance have given military aid to Ukraine, and NATO and Ukrainian troops have participated in joint exercises.

Russian President Vladimir Putin views the alliance’s growing influence in the former Soviet republic as an existential threat. Putin has expressed particular dismay over NATO and U.S. military activities in the Black Sea region.

“The threat on our western borders is, indeed, rising, as we have said multiple times,” Putin said at a ceremony for ambassadors at the Kremlin on Wednesday, The New York Times reported. “In our dialogue with the U.S. and its allies, we will insist on developing concrete agreements prohibiting any further eastward expansion of NATO and the placement there of weapons systems in the immediate vicinity of Russian territory.”

Putin said Russia needed “legal guarantees” that Moscow’s security concerns in the region will be respected.

“We need legal guarantees,” Putin said. “Russia’s legal concerns in the security sphere were ignored, and they now continue to be ignored.”

Meanwhile, Ukraine has said that 90,000 Russian troops have amassed along its border. Russia denies any plans to invade, but the West is not taking Putin’s word for it.

“There is a major risk of Russian military activity in Ukraine in the next few months. All the signs point to a major build-up of military capability,” Ivo Daalder, the U.S. ambassador to NATO from 2009 to 2013, told Insider last week.

NATO Secretary-General Jens Stoltenberg on Wednesday warned Russia that if it invades Ukraine there will be a “high price.” U.S. Secretary of State Antony Blinken has also told Russia that any military incursion into Ukraine could trigger “serious consequences.”

Blinken, who met with other NATO foreign ministers in Latvia this week to discuss the Russia threat, had a meeting with Lavrov at the OSCE conference in Stockholm, Sweden, on Thursday.

The top U.S. diplomat reiterated to Lavrov that the “U.S. and our allies are prepared to impose significant costs” if Moscow chooses the “path of military escalation,” State Department spokesperson Ned Price said in a readout of the meeting. Blinken “underscored that the best path forward is diplomacy,” Price added.

After meeting with his Russian counterpart, Blinken said that President Joe Biden and Putin “may have the opportunity to speak directly in the near future.”

Ukrainian President Volodymyr Zelensky, who recently said he’d uncovered an imminent coup plot involving Russians, has called for direct talks between Moscow and Kiev to end the Donbass conflict. “We must tell the truth that we will not be able to stop the war without direct talks with Russia,” Zelensky said in a Wednesday address to Ukraine’s parliament.

“The war in Donbass has been going on for eight years. Eight years since Russia annexed Crimea,” Zelensky said. “And I’m not afraid to tell everyone about it and speak directly to the Russians. That’s why, at the same time, I’m not afraid to talk to them directly. We are not afraid of direct dialogue.”

The Minsk agreements, which aimed to end the Donbass war, have never been fully enforced and fighting in the region has continued.

This article was written by John Haltiwanger and originally published on Insider.