Tusk's comments come amid increasingly souring relations between the European Union and US, over trade disagreements, the Iran nuclear deal, and the US Embassy's relocation to Jerusalem.
A top European Union official slammed President Donald Trump over his decision to end the Iran nuclear deal on Wednesday morning.
In comments to reporters and a subsequent tweet, he suggested the White House had lost touch with reality.
Looking at the latest decisions of Trump, someone could even think: with friends like that, who needs enemies?
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On Saturday, Merkel told Europeans that the USA had made potential peace in the Middle East "even more difficult" and warned that "the harder the problem is, and the easier the solution is claimed to be, the more suspicious and critical everyone should be". But Europeans are increasingly exasperated by the way Trump is steering US policy, objecting not only to his stances but also to what they say is erratic policymaking that switches on the whim of Fox News programmers.
Options for the EU to protect European companies from negative consequences of the US decision were also needed, Tusk said. "But frankly speaking, Europe should be grateful by President Trump".
He said that the EU leaders should also get an update from EU foreigh policy chief Federica Mogherini, while European Commission President Jean-Claude Juncker will "share his thoughts on how the interests of the European companies engaged in economic cooperation with Iran can be best preserved". "He has made us realize if you need a helping hand, you will find one at the end of your arm".
Iran's foreign minister, Mohammad Javad Zarif, meanwhile said Wednesday that meetings with European Union leaders on salvaging the nuclear deal sent a strong political message but must now be turned into action. Now Europe is faced with the dilemma of maintaining its healthy and growing economic ties with Iran as well as staking a claim for geopolitical independence from the United States and risking sanctions from Washington, or otherwise quietly capitulating and allowing the JCPOA to die. Tusk highlighted the "dramatic events in Gaza" in a letter sent to the European Council before the summit on Tuesday.
The EU is also unimpressed by Trump's decision to place tariffs on European steel and aluminium as part of his "America first" agenda. There appears to have been little progress in those discussions. "It's a moment of truth for Europe", he said. "But we need to be sure that we have done everything in our power, and within the limits of the global trade rules, to avoid a negative scenario", Tusk said.