President Vladimir Putin said Russia will suspend its observation of the New START treaty with the U.S., dealing a blow to the last accord limiting their nuclear arsenals, as he vowed to press on with his faltering invasion of Ukraine.

Russia is fighting for its “historic lands” in Ukraine and “will fulfill the tasks set step-by-step, carefully and consistently,” Putin told the Russian parliament and top officials in Moscow on Tuesday. Russia won’t be the first to resume testing of nuclear weapons as a result of its suspension of New START, though it will do so in response to any U.S. test, he said.

Russia’s suspension of the treaty is “deeply unfortunate and irresponsible,” U.S. Secretary of State Antony Blinken said in Athens. Putin’s decision “makes the world more dangerous” and means the entire infrastructure of arms control has been dismantled, North Atlantic Treaty Organization Secretary General Jens Stoltenberg told reporters in Brussels, urging Russia to reconsider.

President Joe Biden extended the nuclear treaty by five years to 2026 as one of his first acts upon taking office in 2021 shortly before it was due to expire, after Putin had pressed his predecessor Donald Trump without success to agree to a deal.

The Biden administration will “be watching carefully to see what Russia actually does” and ensure the U.S. is “postured appropriately for the security of our own country and that of our allies,” Blinken said. The extension of New START was in the security interests of both countries and “we remain ready to talk about strategic arms limitations at any time with Russia, irrespective of anything else going on, in the world or in our relationship.”

The U.S. and its NATO allies “want to inflict a strategic defeat on us and crawl into our nuclear facilities” by demanding inspections under the treaty, Putin said, describing the requests as absurd.

The State Department accused Russia last month of breaching the terms of the treaty by refusing to allow inspectors on its territory and stonewalling U.S. efforts to discuss the issue. Russia dismissed the criticisms and blamed the U.S., saying difficulties with New START were “a direct result of the hybrid war unleashed by the West against our country.”

Putin gave his first stateof- the-nation address in nearly two years as Russia’s war in Ukraine nears the 12-month mark on Feb. 24. He spoke on the anniversary of his decision to recognize Russian-backed separatists in Ukraine’s Donetsk and Luhansk regions as independent, whose defense he used as the excuse to mount the full-scale invasion.

Despite the anticipation, the speech lasting nearly two hours covered mainly Putin’s usual efforts to shift the blame for the conflict to the U.S. and its allies, where he claimed godlessness and pedophilia have become “the norm.” Much of the address also focused on domestic issues, with new benefits offered for veterans and their families, as well as defense workers.

Russia’s suspension of New START means the U.S. could lose access to inspections and monitoring data about the number of deployed Russian nuclear warheads, as well as the land- and seabased vehicles used to launch them. About 200 inspectors drawn from the Department of Defense, intelligence community and State Department are assigned to carry out verification under the treaty, according to Steven Pifer, the former U.S. ambassador to Ukraine who conducted arms-control negotiations with Russia.

“What the Pentagon values most about the treaty isn’t the numbers, it’s the transparency,” said Pifer, who’s now a fellow at the Brookings Institution.

Even after last year’s mutual accusations between Moscow and Washington that the other side was hindering inspections, nucleararms data continued to flow, according to Pifer. The U.S. receives about 2,000 notifications a year, informing security officials about the status of Russian forces. Sides update and exchange bilateral data every six months.

“The suspension of participation in the New START treaty is a very hostile signal,” said Andrey Kolesnikov, a political analyst at the Carnegie Center. “There’s no hope for restoring relations with the West and he intends to continue the war at any price.”

Putin’s speech “is an address to the ‘good West’ (society and the pragmatic elites) and friendly countries about how the policies of the ‘bad West’ is leading to the complete destruction of the old architecture of global security and puts the whole world at risk,” said Tatiana Stanovaya, founder of R.Politik, a political consultant.

Ukraine’s U.S. and European allies want “to transform a local conflict into a phase of global confrontation,” Putin said in a speech repeatedly interrupted by applause. “We understand this and will respond accordingly because in this case we’re talking about the existence of our country.”

Having failed with initial plans to seize Ukraine’s capital, Kyiv, within days, Russia’s military has suffered repeated defeats and massive casualties at the hands of Ukrainian forces backed by U.S. and European weapons supplies.

As intense battles of attrition go on in eastern Ukrainian regions with neither side making much progress for months, Ukrainian President Volodymyr Zelenskyy appealed at a security conference in Munich at the weekend for the U.S. and its allies to speed up weapons deliveries to help counter a Russian spring offensive and allow his forces to take the initiative in the fight.

Putin gave his address a day after Biden made a surprise visit to Kyiv to underline continued American support for Ukraine. The U.S. president is due to make a speech in Poland later Tuesday.

The Kremlin leader has shrugged off rising Russian casualties and is steeling the country and its economy for a long war. He called up 300,000 troops in a partial mobilization in September and has sought to convince Russians that his unprovoked attack on Ukraine is an existential struggle with the “collective West” for their country’s survival, repeatedly comparing it to the Soviet Union’s victory in World War II.

____ (With assistance from Courtney McBride and Jonathan Tirone.)