NATO Secretary General Mark Rutte has told Europe it should “keep on dreaming” if it thinks it can defend itself without the support of the United States.

“If anyone thinks here again that the European Union, or Europe as a whole, can defend itself without the US, keep on dreaming. You can’t. We can’t. We need each other,” Rutte said during an address to the European Parliament in Brussels on Monday.

The NATO chief warned European nations they would need to increase defense spending to 10% if they “really want to do it alone,” adding they would need to build up their own nuclear capability, costing billions of euros.