WASHINGTON

Russia's efforts to intimidate NATO allies into halting support for Ukraine have had the "opposite effect," the head of the alliance said Thursday.

It came after a bombshell report suggested the Kremlin sought to assassinate the CEO of a major German arms manufacturer

Jens Stoltenberg declined to comment on the report but acknowledged that NATO is aware of "a Russian attempt to intimidate us from providing support" for Kyiv as it continues to combat a Russian invasion that has persisted well over two years.

"But we see that it has, if anything, the opposite effect on NATO allies. They're actually stepping up their support for Ukraine," he told reporters during a news conference with Ukrainian President Volodymyr Zelenskyy.

"We have seen arrests across the alliance, in the United Kingdom, in Germany, in Poland, in the Baltic countries, following these hostile actions, and, of course, the ongoing legal processes. And what NATO does is also to increase intelligence sharing, to help allies to protect against these actions," added Stoltenberg.

CNN reported Wednesday that US and German intelligence agencies thwarted a plot to kill Armin Papperger, the CEO of German arms firm Rheinmetall.

Rheinmetall is Germany's largest and most successful manufacturer of 155mm artillery shells, which are deemed vital in Ukraine's war against Russia. The company is set to open an armored vehicle plant in Ukraine in the coming weeks, an effort, said one intelligence source who spoke to CNN, that is particularly troubling to Russia.

The report said Moscow has been conducting a sabotage campaign throughout Europe, primarily through proxies, for more than six months.

Stoltenberg maintained that allies "have the right to help and uphold Ukraine's right of self-defense."

"And the right of self-defense includes also the right to strike legitimate military targets on the territory of the aggressor, Russia," he added, noting that some allies have recently loosened restrictions on the use of their arms to strike targets in Russia while others “have not imposed any restrictions at all.”

That includes actions from the US, Germany and the UK -- all did so to varying degrees beginning in May.

"I think it's important to remember what this is. This is a war of aggression launched by Russia against a democratic, friendly neighbor, Ukraine. Russia invaded Ukraine. That's a blatant violation of international law," he added.

Zelenskyy urged allies to lift all remaining restrictions “if we want to win, if we want to prevail,” and maintain their support for his country, saying that a Russian victory would shatter the established rules-based international order.

"It is Russia that invaded our land. It's Russia that wants to take our lives. It's Russia that kills and destroys through this war against Ukraine. It wants to show what awaits other countries if we do not endure," he said. "That is why we must endure. That is why we must preserve our unity, all partners, and that is why we must transcend ourselves so that Russia does not succeed in making the world accept the notion that wars of aggression are normal."

The Ukrainian president said that during the summit there were "concrete successes" agreed to for Ukraine, including announcements to contribute five Patriot air defense batteries and dozens of other systems, as well as a new security agreement.

Allies are also expected to sign a new compact with Ukraine.