European Council President Donald Tusk on Tuesday appealed to the Trump administration to respect and appreciate its allies, Xinhua reported.

"Dear America, appreciate your allies, after all, you don't have that many," Tusk said, after the European Union (EU) and the North Atlantic Treaty Organization (NATO) signed a joint declaration aimed at enhancing military cooperation.

"And, dear Europe, spend more on your defense, because everyone respects an ally that is well-prepared and equipped," Tusk said following the signing ceremony.

"Money is important, but genuine solidarity is even more important," stressed Tusk, adding that he hopes U.S. President Donald Trump keep that in mind when they meet at the upcoming NATO summit.