NATO chief Mark Rutte warned Monday that Europe cannot defend itself without the United States, pushing back against renewed calls for the continent to stand on its own after tensions rose over Greenland.

"If anyone thinks here that the European Union, or Europe as a whole, can defend itself without the U.S., keep on dreaming. You can't. We can't. We need each other," he said during his address at the European Parliament's Committee on Foreign Affairs and Committee on Security and Defense in Brussels.

He added that the U.S. also relies on NATO to ensure its own security, emphasizing the mutual dependence among NATO allies.

"If you really want to go it alone, and those who you are pleading for that, forget that, you can never get there with 5%, it will be 10%.

"You have to build up your own nuclear capability that costs billions and billions of euros. You will lose, then, in that scenario, you would lose the ultimate guarantor of our freedom, which is the U.S. nuclear umbrella. So, hey, good luck," he added.