It would be the end of NATO if the U.S. took Greenland by force and European Union member states are under obligation to come to Denmark's assistance if it was faced with military aggression, the European Commissioner for Defence and Space said on Monday.

"I agree with the Danish Prime Minister that it will be the end of NATO, but also among people it will be also very, very negative," Commissioner Andrius Kubilius told Reuters at a security conference in Sweden.