NATO Secretary-General Jens Stoltenberg has said the alliance will "not be intimidated" by Russia's "nuclear rhetoric" after a two-day meeting of the alliance's defense ministers in Brussels.
Stoltenberg on October 13 called the rhetoric dangerous and reckless, and said that Russia knows that the use of a nuclear weapon against Ukraine "will have severe consequences."
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Stoltenberg declined to give any details on NATO's potential response but said even the use of a small nuclear weapon would be very serious, "fundamentally changing the nature of the war in Ukraine."
Stoltenberg also said NATO would monitor Russia's annual nuclear drills very closely, as it has done for decades.
The NATO chief was apparently referring to annual exercises in which Russia tests its nuclear-capable bombers, submarines, and missiles. The exercise normally takes place in late October.
NATO has vowed to go ahead with its own nuclear exercise next week. Dubbed Steadfast Noon, it will involve NATO-member air forces flying training flights without live weapons to practice how to use U.S. nuclear bombs based in Europe.
Canceling the drills because of the war in Ukraine would have sent a "very wrong signal," Stoltenberg said earlier this week.
Recent Russian military setbacks in Ukraine have raised concerns that President Vladimir Putin might follow through on threats to use nuclear weapons.
SEE ALSO: Russian Strikes Kill Five In Southern Ukrainian City As NATO Partners Pledge More Military AidEuropean Union foreign policy chief Josep Borrell echoed Stoltenberg in sending his own strong message to the Kremlin in response to Putin's veiled threats about the use of nuclear weapons.
"Any nuclear attack against Ukraine will create an answer, not a nuclear answer, but such a powerful answer from the military side that the Russian Army will be annihilated," Borrell said.
The NATO alliance has stopped short of threatening to use its nuclear arsenal to respond, as Ukraine is not covered by its mutual self-defense clause.
Earlier on October 13, U.S. Defense Secretary Lloyd Austin reaffirmed Washington's commitment to defend "every inch" of NATO territory.
Austin spoke shortly before attending a meeting by NATO's Nuclear Planning Group, which is the alliance's senior body on nuclear issues and handles policy associated with its nuclear forces.
On the sidelines of the meeting, a group of 13 NATO members and Finland, which is in the process of joining the alliance, signed a letter of intent to procure air defense systems such as the Arrow 3 and Patriot.
Some NATO members have been looking to improve their air-defense systems in the wake of Russia's unprovoked war in Ukraine. Others need to replace or upgrade systems after giving weaponry to Ukraine.
On October 12, the Ukraine Defense Contact Group comprising some 50 countries announced at a meeting in Brussels the delivery of new air defenses and committed more military aid to Kyiv to protect against Russia's indiscriminate missile attacks across the country.
Russia has launched waves of missile strikes on several regions of Ukraine for four days in a row, bombing multiple cities, including Kyiv, as reprisals for a blast at the weekend that damaged the only bridge between Moscow-annexed Crimea and mainland Russia.
Pledges from allies included an announcement by France that it would deliver radar and air defense systems to Ukraine in the coming weeks. Canada said it would provide artillery rounds and winter clothing among other supplies.
Germany has sent the first of four planned IRIS-T SLM air-defense systems, while Washington said it would speed up delivery of a promised NASAMS air-defense system.