Although additional sanctions against Russia may be stalled, current sanctions are set to be maintained.
Former Polish prime minister Tusk said that ''when we are united, we will be able to put a stop to the aggressive policy of Russia against her neighbours.''
President Barack Obama affirmed that ''we are all committed to making sure that we uphold the basic principles of sovereignty and territorial integrity that have been threatened by Russian aggression.
''We have been able to maintain strong unity with respect to sanctions,'' he added.
Tusk noted that besides Ukraine, the question of unity was also key with regards to jihadist threats and negotiations on the Transatlantic Trade and Investment Partnership (TTIP).
''Although these are three different - very different challenges, they have a common denominator, I think.
''It’s a need, maybe greater than ever before, a need for unity of Europe and the United States.
''We are I think today calling into question even our fundamental values, like freedom, freedom of democracy, prosperity and, for sure, the political order.
''Today, we can see with full clarity that they [our enemies] are trying to divide us, from inside of Europe, as well as Europe and America.
Tusk claimed that ''the past has shown that when we were united we were able to successful fight against terrorism.
''We have to stop violent extremism spreading in Africa,'' he continued.
Referring to Libya, he argued that ''we must help because we cannot have a failed state run by warlords and anarchy — sitting in anarchy just 100 miles off the southern coast of Europe.''
Tusk also stressed that ''we achieved success ''having acted together in the field of the economy and free trade.''
He concluded that that ''who we are tomorrow depends on what we do today,'' claiming that ''now is the best time [to act] through some kind of renaissance of faith in our community.
''And you Americans express this need I think in the most convincing phrase I know, 'United we stand, divided we fall.' I am convinced it's true.'' (nh)