Speaking at a news conference, Tusk said he had spoken at length earlier in the day with German Chancellor Friedrich Merz, who briefed him on the discussions held in London on Sunday with British Prime Minister Keir Starmer, French President Emmanuel Macron and Zelensky.
"From Poland's point of view, no arrangements in which Poland does not participate will be respected by us, meaning they will not be binding on us," Tusk said.
He argued that Poland is an indispensable partner in discussions about Ukraine's future and the security of the region.
Tusk also said he spoke on Monday with Italian Prime Minister Giorgia Meloni, who he suggested was dissatisfied with the so-called E3 format involving Britain, France and Germany.
He said a broader meeting including Poland and Italy would be held in the coming days.
Tusk also expressed caution about proposals for a rapid opening of talks with Russian President Vladimir Putin on ending the war in Ukraine.
"It must be absolutely clear that nobody in Europe should play the role of an arbiter between Russia and Ukraine," he said. "In this war, we are on Ukraine's side. Ukraine cannot lose this war, and Russia cannot win it."
Despite occasional disagreements among European allies, Tusk said there was broad unity in support of Ukraine.
Poland will continue to participate wherever its presence is "necessary and needed," he added, describing diplomacy over Ukraine as a complex contest among major powers and ambitious states seeking influence over Europe's security.
(gs)
Source: IAR, PAP