In an interview on Russian state television, Foreign Minister Sergey Lavrov said the possibility of nuclear war “should not be underestimated” and added that “under no circumstances should a Third World War be allowed to happen.”

“What is the U.S. and European diplomatic strategy for bringing an end to the war and deterring further aggression that is backed by nuclear threats?”

“The risk is serious, real,” said Lavrov. “There can be no winners in a nuclear war.”

Lavrov went on to argue that by heavily arming Ukraine as it combats Russia’s illegal and deadly invasion, NATO members are, “in essence, going to war with Russia through a proxy.”

Dmytro Kuleba, Ukraine’s foreign minister, replied that Lavrov’s “talk of a ‘real’ danger of WWIII” is part of Moscow’s effort to “scare the world off supporting Ukraine.”

“This only means Moscow senses defeat in Ukraine,” Kuleba wrote in a Twitter post on Monday. “Therefore, the world must double down on supporting Ukraine so that we prevail and safeguard European and global security.”

The Russian foreign minister’s remarks aired hours after U.S. Secretary of State Antony Blinken and Pentagon chief Lloyd Austin visited Kyiv to reiterate the Biden administration’s intention to continue supplying Ukraine with advanced weaponry.

While far from alone, the U.S. has been Ukraine’s top weapons provider, authorizing nearly $4 billion worth of Javelin anti-tank missiles, drones that explode on impact, and other equipment.

During the visit, Austin said that the Biden administration’s objective in Ukraine is to “see Russia weakened to the point where it can’t do things like invade Ukraine”—a statement that appeared to confirm anti-war critics’ concerns that the U.S. is more interested in damaging Russia than achieving a peaceful resolution to the devastating war, which has sparked a massive humanitarian crisis with global consequences.

“What is the U.S. and European diplomatic strategy for bringing an end to the war and deterring further aggression that is backed by nuclear threats?” Daryl Kimball, director of the Arms Control Association asked Tuesday in response to Austin’s comments.

In a column last month, The Intercept‘s Jeremy Scahill wrote that “it may be the case that the flow of Western weapons to the Ukrainian forces will so bleed Russia that it pulls out of Ukraine, fatally damaging [Russian President Vladimir] Putin’s grip on power and saving many lives.”

“But if it doesn’t, and the flow of weapons delays a negotiated settlement between Russia, Ukraine, and NATO,” Scahill added, “then it is hard to see the massive scope of the weapons transfers as a clear positive.”

Austin later addressed Lavrov’s interview, saying that “nobody wants to see a nuclear war.”

“Nobody can win it,” Austin added. “There’s always a possibility a number of things can happen but I think it is unhelpful and dangerous to rattle sabers and speculate about the use of nuclear weapons.”

As the New York Times reported Monday, the Biden administration is relying “on American defense contractors to scour Eastern European munitions factories to find newly made weapons designed by the United States’ former adversary, the Soviet Union, to fulfill President Biden’s pledges of increased military aid for Ukraine.”

The accelerating flow of advanced weaponry into Ukraine comes amid fears that the prospects of a diplomatic resolution to Russia’s war are dimming. Earlier this month, Putin said peace talks between Russian and Ukrainian delegations are at a “dead end” as Moscow ramped up its attacks on eastern Ukraine.

Peace advocates have been warning since the start of Russia’s full-scale assault on Ukraine in February that the invasion heightens the threat of nuclear catastrophe. Nuclear weapons manufacturers have seen their share prices surge since Russia launched its invasion, which began with Putin issuing an ominous threat of nuclear strikes against any country that interferes.

The Biden administration, meanwhile, has faced criticism for keeping a nuclear first strike by the U.S. on the table in its Nuclear Posture Review.

“Putin is threatening the first use of nuclear weapons to hold Ukraine hostage and keep the U.S. and NATO out,” Tom Collina, policy director at the Ploughshares Fund, said earlier this month. “This is nuclear blackmail, and it’s a dangerous precedent that we must oppose.”

“It’s therefore deeply disappointing that the Biden administration just missed a key opportunity to reject first use,” Collina added. “Instead, Biden’s policy also allows first use and is essentially the same as Russia’s, and this undermines Biden’s ability to build international opposition to what Putin is doing.”