NATO Chief Jens Stoltenberg on June 12 described the "ongoing adaptation" of the military alliance's nuclear arsenal, in a rare reference to the weapons which he described as the "ultimate security guarantee."
Speaking to reporters ahead of a two-day meeting of the bloc's defense ministers in Brussels, Stoltenberg highlighted escalating tensions and increasing rhetoric from the Kremlin.
"What we have seen over the last years and months is dangerous nuclear rhetoric from the Russian side.... We also see some more exercises, nuclear exercises on the Russian side," he said in comments reported by Reuters.
NATO officials rarely comment on the alliance's nuclear arsenal, but Stoltenberg said the U.S. was modernizing its nuclear weapons stationed in Europe.
He also referenced announcement in May that F-35 fighter jets had taken over the nuclear role of the Netherlands within NATO from the F-16.
The comments come as tension continue to rise between Russia and the West.
The United States may have to increase its deployment of strategic nuclear weapons amid growing threats from China, Russia, and other adversaries, a White House official said on June 7.
Russia and Belarus launched the second stage of tactical weapons nuclear drills this month, the Kremlin's Defense Ministry said on June 11.
"The situation on the European continent is quite tense, which is provoked every day by new decisions and actions of European capitals hostile to Russia, and above all by Washington," Kremlin spokesman Dmitry Peskov said in comments reported by Reuters.
Last month Russia said the exercises were a response to what it described as "provocative statements and threats by certain Western officials against the Russian Federation."
Russian President Vladimir Putin has repeatedly made nuclear threats against Ukraine and the West since the beginning of the full-scale invasion in February 2022.
The threats have failed to materialize, and Russia continues to wage its all-out war without using its nuclear arsenal.