GENEVA

NATO Secretary-General Mark Rutte urged stronger transatlantic unity Wednesday, warning that neither Europe nor the US can tackle global security threats alone.

Rutte acknowledged tensions within the alliance, including disputes about trade and discussions around European strategic autonomy. But he stressed that the complex challenges require collective strength.

"There are difficult debates between Europe and America over trade and tariffs, and there are calls to revive ideas of European autonomy," he said at the Warsaw School of Economics.

"Let me be absolutely clear: this is not the time to go it alone, not for Europe or North America. The global security challenges are too great for any of us to face on our own."

Russia's war against Ukraine is raging, he said, and added that there are concerns about how it will end.

"However it ends, Russia will remain the most significant and direct threat to our security," said Rutte.

He emphasized NATO's irreplaceable role in defending the Euro-Atlantic area, highlighting the vital contributions of countries like the US, UK, Türkiye, Canada, Norway and Iceland.

"It is impossible to imagine the defense of Europe without them. And nothing can replace America's nuclear umbrella -- the ultimate guarantor of our security."

While reaffirming the importance of US engagement, Rutte made it clear that European allies must also deliver.

"Europe needs to know that Uncle Sam still has our back," he said. "But America also needs to know that its NATO allies will step up and play their full part without restrictions and without capability gaps. It's only fair. Reassurance is a two-way street," he said.

He added that NATO has the strategies, capabilities and coordination needed to defend member states and support Ukraine in its fight against Russian aggression.

"Together in NATO, Europe and North America are unbeatable today and in the future," he said.

Rutte concluded with a strong message of confidence in the alliance's direction.

"Be assured, the transatlantic bond is strong. And yes, we will make NATO a stronger, fairer, and more lethal alliance. That is how we all stay safe in a more dangerous world," he added.

Rutte noted the priorities for a NATO summit at The Hague in July, saying the alliance will need to do "even more" to ensure all allies do their fair share "based on ambitious new targets for all NATO allies, strengthening our capabilities, readiness and deterrence, including air and missile defense, long-range missiles and more ground forces."

"This will enable Europeans to take on a greater share of our collective defense, while maintaining strong American commitment and presence in Europe," he said.

Rutte said the whole alliance is "on the eastern flank," only the formal eight countries.

"It is important to realize this, and (Russian President Vladimir) Putin has to know that when he would try to get a square kilometer of Estonia, Poland, Slovakia, or of Spain, Portugal, for that matter, our reaction will be devastating, that the full-on spot of NATO will be upon him," he said.