Russian President Vladimir Putin declared Tuesday that Moscow was suspending its participation in the New START treaty — the last remaining nuclear arms control pact with the United States — sharply upping the ante amid tensions with Washington over the fighting in Ukraine.

Speaking in his state-of-the-nation address, Putin also said that Russia should stand ready to resume nuclear weapons tests if the U.S. does so, a move that would end a global ban on nuclear weapons tests in place since Cold War times.

Explaining his decision to suspend Russia’s obligations under New START, Putin accused the U.S. and its NATO allies of openly declaring the goal of Russia’s defeat in Ukraine.

“They want to inflict a ‘strategic defeat’ on us and try to get to our nuclear facilities at the same time,” he said, declaring his decision to suspend Russia’s participation in the treaty. “In this context, I have to declare today that Russia is suspending its participation in the Treaty on Strategic Offensive Arms.”

New START’s official name is The Treaty between the United States of America and the Russian Federation on Measures for the Further Reduction and Limitation of Strategic Offensive Arms.

NATO Leader Expresses Concern

NATO Secretary-General Jens Stoltenberg voiced regret about Putin’s move, saying that “with today’s decision on New START, full arms control architecture has been dismantled.”

“I strongly encourage Russia to reconsider its decision and respect existing agreements,” he told reporters.

Putin argued that while the U.S. has pushed for the resumption of inspections of Russian nuclear facilities under the treaty, NATO allies had helped Ukraine mount drone attacks on Russian air bases hosting nuclear-capable strategic bombers.

The Russian military said that it shot down the Soviet-built drones that struck two bomber bases deep inside Russia in December, but acknowledged that several servicemen were killed by debris that also damaged some aircraft.

Putin on Tuesday mocked NATO’s statement urging Russia to allow the resumption of the U.S. inspections of Russian nuclear weapons sites as “some kind of theater of the absurd.”

“The drones used for it were equipped and modernized with NATO’s expert assistance,” Putin said. “And now they want to inspect our defense facilities? In the conditions of today’s confrontation, it sounds like sheer nonsense.”

He said that a week ago he signed an order to deploy new land-based strategic missiles and asked: “Are they also going to poke their noses there?”

The Russian leader also noted that NATO’s statement on New START raises the issue of the nuclear weapons of Britain and France that are part of the alliance’s nuclear capability but aren’t included in the U.S.-Russian pact.

“They are also aimed against us. They are aimed against Russia,” he said. “Before we return to discussing the treaty, we need to understand what are the aspirations of NATO members Britain and France and how we take it into account their strategic arsenals that are part of the alliance’s combined strike potential.”

Putin emphasized that Russia is suspending its involvement in New START and not entirely withdrawing from the pact yet.

The New START treaty, signed in 2010 by U.S. President Barack Obama and Russian President Dmitry Medvedev, limits each country to no more than 1,550 deployed nuclear warheads and 700 deployed missiles and bombers. The agreement envisages sweeping on-site inspections to verify compliance.

Just days before the treaty was due to expire in February 2021, Russia and the United States agreed to extend it for another five years.

Russia and the U.S. have suspended mutual inspections under New START since the start of the COVID-19 pandemic, but Moscow last fall refused to allow their resumption, raising uncertainty about the pact’s future. Russia also indefinitely postponed a planned round of consultations under the treaty.

The U.S. State Department has said that Russia’s refusal to allow the inspections “prevents the United States from exercising important rights under the treaty and threatens the viability of U.S.-Russian nuclear arms control.” It noted that nothing prevents Russian inspectors from conducting inspections of U.S. facilities.

Putin on Tuesday challenged the U.S. assertion, alleging that Washington has rejected some Russian requests for visits to specific U.S. facilities.

“We aren’t allowed to conduct full-fledged inspections under the treaty,” he said. “We can’t really check anything on their side.”

He alleged that the U.S. was working on nuclear weapons and some in the U.S. were pondering plans to resume nuclear tests banned under the global test ban that took effect after the end of the Cold War.

“In this situation, Rosatom (Russia’s state nuclear corporation) and the Defense Ministry must ensure readiness for Russian nuclear weapons tests,” Putin said. “We naturally won’t be the first to do it, but if the U.S. conducts tests we will also do it. No one should have dangerous illusions that the global strategic parity could be destroyed.”