BRUSSELS — NATO Secretary General Jens Stoltenberg insists that despite the "demise” of the Intermediate-range Nuclear Forces Treaty (INF), avoiding a new arms race with Russia is possible.

But, speaking in Brussels on Friday, he said this depended entirely on Moscow “changing its behavior.”

“We will not mirror what Russia does and we do not want a new arms race," Stoltenberg said. NATO continues to aspire to a constructive relationship with Russia, but at same time we must ensure we have a credible defense.”

Speaking specifically about the end of the INF, Stoltenberg added: “Today is the day when we see the final demise of the treaty and I regret that. However, we must find a right balance between being strong but without over reacting or reaching conclusions too quickly.We will react in a prudent and responsible way.”

He also placed the blame on Moscow for the expiration of the INF treaty, a landmark agreement of Cold War-era arms control signed by Soviet leader Mikhail Gorbachev and U.S. President Ronald Reagan in 1987. The 1987 pact banned ground-launched nuclear and conventional ground-launched ballistic and cruise missiles with ranges of 310 to 3,400 miles.

By banning medium-range land-based missiles, which are capable of reaching Russia from Western Europe and vice versa, the treaty aimed to avert an arms race on the continent. The United States announced last year it was withdrawing from the pact, accusing Russia of failing to comply. Moscow denies it has violated the treaty and says Washington is withdrawing because it wants to pursue a new arms race.

But Stoltenberg told reporters, “Russia today remains in violation of the treaty, despite years of U.S. and allied engagement, including a final opportunity over six months to honor its treaty obligations. As a result, the United States decision to withdraw from the treaty, a decision fully supported by NATO allies, is now taking effect.”

“I welcome the fact that NATO is united on this all the way and that all allies agree with the U.S approach. I am confident we will stay united.”

Russia, he insisted, bears “sole” responsibility for the treaty’s demise, adding that he “regrets” that Russia has shown “no willingness and taken no demonstrable steps to return to compliance with its international obligations.”

“A situation whereby the United States fully abides by the treaty, and Russia does not, is not sustainable,” he noted, confirming that NATO will respond in a “measured and responsible” way to the “significant risks” posed by the Russian 9M729 missile.

The Trump administration issued formal protests that the new Russian missile had been tested at ranges prohibited under the treaty. Stoltenberg said the deployment was part of a “broader pattern,” with Russia also more recently investing in new and advanced defense capabilities.

“Allies are firmly committed to the preservation of effective international arms control, disarmament and non-proliferation,” he said. "Therefore, we will continue to uphold, support, and further strengthen arms control, disarmament, and non-proliferation, as a key element of Euro-Atlantic security.”