Ukraine says it shot down six Kinzhal missiles over Kyiv fired by Russia, demonstrating the effectiveness of Western air defenses and potentially changing the calculus over what kind of nuclear risk Moscow poses in the war it started.

The six Kh-47 missiles launched from MiG-31K aircraft were among a volley of 18 missiles Russia fired at Ukraine overnight. Three cruise missiles were fired from land, and a further nine Kalibr cruise missiles were launched from the Black Sea.

The commander-in-chief of Ukraine’s armed forces, Valeriy Zaluzhnyi, said all had been successfully intercepted. Moscow has boasted that the Kinzhals, which are nuclear capable and travel at up to 10 times the speed of sound, are unstoppable.

“This is not the first Russian weapon which has been called unstoppable by the Russians and it has been revealed as pretty much stoppable,” said Sergej Sumlenny, founder of the European Resilience Initiative Center, a German think tank.

“This has devastating consequences for the credibility of the Russian army and of Russian technology,” he told Newsweek. “Normally an air defense should be oversaturated during these attacks.”

“We know now that the Ukrainians, with the help of Western equipment, are capable of fighting back the most severe Russian attack with the most modern Russian weapon the Russians have ever used against Ukraine.”

“In the West, the fear of possible nuclear escalation is still very high,” said Sumlenny, “but we need to seriously rebalance our weighting of all the risks.”

Kyiv’s purported success in intercepting the Russian missiles means the possibility of a successful nuclear attack by Russia “should be seen as significantly lower compared to what we believed,” added Sumlenny.

Since the start of the war, Russian state television has frequently invoked Russia’s nuclear capabilities. President Vladimir Putin has hinted at nuclear escalation and mixed messaging from Moscow, which has denied such weapons would be used, keeps world leaders guessing.

Fabian Hoffman, doctoral research fellow at the University of Oslo, told Newsweek that Kyiv’s ability to intercept missiles in such an intense, time-coordinated, multi-vector attack indicates “that even if you arm these delivery vehicles with tactical nuclear warheads, there is a decent chance that they will not land at their target.”

“I think this will cause Russian decision makers to ask some difficult questions and they may feel less secure about the survivability and the deliverability of their nuclear arsenal,” he said.

While this should not encourage the West to be more willing to risk nuclear escalation, “I also don’t think a nuclear confrontation would be in the interest of Russia.”

Ukraine said that earlier in May it had shot down a single Kinzhal missile over Kyiv for the first time, using an American-supplied Patriot air defense system.

The Patriot is among advanced air defense systems NATO countries have given Kyiv. The German Iris-T arrived in October and has since shot down more than 60 targets. The Franco-Italian SAMP/T has also recently arrived.

It is unclear whether the Patriot system intercepted all the missiles fired overnight but the purported success of Ukraine’s military points to it having a reliable defense network that can withstand a barrage described by Serhiy Popko, the head of Kyiv’s military administration, as “exceptional in its density.”

Putin billed the Kinzhal, which is the Russian word for “dagger”, as a next-generation Russian weapon, although Moscow’s claims about its capabilities, including that it could evade sophisticated air defense systems, have been questioned by experts.

The Russian Ministry of Defense said it fired a Kinzhal missile at a munitions depot around Deliatyn, southwestern Ukraine, on March 19, 2022, in the first known use of the weapon in combat. Newsweek has contacted the Russian Defense Ministry for comment.