Tusk spoke to reporters as leaders from the EU's 27 member states gathered in Brussels for a special summit focused on transatlantic relations.
European Council President Antonio Costa convened the meeting after Trump threatened to impose new tariffs on goods from eight EU countries amid his push to acquire Greenland.
"For us, the United States is absolutely the most important partner when it comes to security," Tusk said.
He added that Europe must safeguard its relationship with Washington while speaking with a single voice.
Germany's Merz 'grateful' for Trump's U-turn on Greenland, tariffs
Meanwhile, German Chancellor Friedrich Merz said he welcomed a change in Trump’s position on Greenland, after concerns that a dispute over the Arctic island could strain NATO unity, Germany's DPA news agency reported.
"I am very grateful that President Trump has refrained from his original plans to take over Greenland. And I am also grateful that he has refrained from imposing additional tariffs on February 1," Merz told reporters ahead of the Brussels meeting.
German Chancellor Friedrich Merz. Photo: PAP/Wiktor Dąbkowski
Trump said on Wednesday he would not impose tariffs on eight European countries as planned, citing progress toward an agreement on Greenland and Arctic security following talks with NATO Secretary-General Mark Rutte at the World Economic Forum in Davos, Switzerland.
Polish President Karol Nawrocki attended a signing ceremony for Trump’s Board of Peace initiative on Thursday but did not sign the organisation’s founding charter, he told reporters in Davos.
The initiative was initially presented as part of Trump’s plan to end the war in Gaza but is now widely seen as having a broader global role, raising concern in Europe and elsewhere that it could rival or undermine the United Nations.
Trump on Wednesday called for immediate negotiations to acquire Greenland, saying in a speech in Davos that he would not use force in pursuing control of the mineral-rich Arctic island.
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Source: IAR, PAP, TVP Info, Reuters, DPA