Secretary General Jens Stoltenberg said Tuesday NATO had not noticed any differences in Russia's nuclear posture despite recent remarks from Russian President Vladimir Putin.

Nevertheless, the military alliance needed to remain "vigilant," he said.

"While Russia is increasingly resorting to horrific and indiscriminate attacks on civilians and critical infrastructure, President Putin is failing in Ukraine," Stoltenberg told a news conference on the eve of a meeting of NATO defense ministers in Brussels.

The NATO head also said that Putin started the war by invading Ukraine, and it is therefore up to the Russian president to end the conflict by withdrawing troops.

'Russia is actually losing on the battlefield,' says Stoltenberg

Stoltenberg, whose comments come after two days of intensified Russian missile strikes on Kyiv and other Ukrainian cities, said: "I think what we saw yesterday is actually a sign of weakness, because the reality is that they are not able to make progress on the battlefield. Russia is actually losing on the battlefield."

Leaders of the Group of Seven (G7) nations held a virtual meeting on Tuesday with Volodymyr Zelenskyy after the Ukrainian president spoke with German Chancellor Olaf Scholz about increasing pressure on Russia as well as military aid for Kyiv.

"With a difficult winter ahead it is even more important that North America and Europe continue to stand united in support for Ukraine and in defense of our people," Stoltenberg said.

NATO nuclear response exercise to go ahead

Meanwhile, NATO will carry out its annual nuclear response training exercise "Steadfast Noon" next week as planned, Stoltenberg told reporters.

"This is routine training which happens every year to keep our deterrent safe, secure and effective," he said. "Russia knows that a nuclear war cannot be won and must never be fought," Stoltenberg said referring to the Kremlin's "veiled nuclear threats."

President Putin has threatened to protect Russian soil using any and all measures necessary — including using nuclear weapons. Moscow recently annexed four Ukrainian regions, in violation of international law, and Putin has said Russia would see Ukrainian attacks on these regions as attacks on Russia itself.

NATO 'doubles' Baltic and North Sea presence

The alliance has bolstered its naval deployments to protect its infrastructure after "sabotage" on the Nord Stream gas pipeline, with Stoltenberg saying: "We have doubled our presence in the Baltic and North seas to over 30 ships supported by maritime patrol aircraft and undersea capabilities."

Germany's federal public prosecutor on Monday announced the start of an investigation into leaks after massive amounts of gas were released into the Baltic Sea when both lines were ruptured on September 26.

It is suspected by many in the West that the leaks were caused by explosives placed near the pipelines, which deliver Russian natural gas to Germany.

jsi/rs (Reuters, dpa, AFP)