EU Council President António Costa and European Commission President Ursula von der Leyen joined President Volodymyr Zelensky at the commemoration, alongside foreign delegations including senior Polish officials.
At a joint press conference, Zelensky thanked the EU leaders personally for travelling to Kyiv on the anniversary.
"Europe has stood with us throughout these difficult years, and our people trust Europe – they know we are not alone," he said.
Zelensky then urged Europe to do more – banning Russia's shadow fleet from European waters, ending imports of Russian oil and gas, and stepping up arms deliveries to Ukraine.
"We count on the 20th sanctions package being strong and efficient. It must be adopted as soon as possible."
Zelensky said a clear date for EU membership was, in his view, "a key geopolitical security guarantee for Ukraine", adding that 2027 was a target he considered both "very important and doable, so that Putin cannot block our membership for decades".
Von der Leyen acknowledged that Ukraine was making impressive progress on reforms despite fighting a war for its survival, but said setting a specific date for membership was not something the EU was in a position to do, while insisting that support for Ukraine's accession is "absolutely clear".
The EU's Commission chief also signalled a further round of economic pressure on Moscow.
"We will soon get our 20th sanctions package over the line," she said.
"Our sanctions will keep draining Russia's revenues and weakening its war machine."
Polish officials weigh in on Ukraine's EU bid
Earlier, Polish lower-house Speaker Włodzimierz Czarzasty addressed the Ukrainian parliament in Kyiv, telling MPs that EU membership was one of the most important security guarantees Ukraine could have.
"Poland supports these aspirations with all its strength. You will be in the European Union," he said.
Foreign Minister Radosław Sikorski, also present in Kyiv, said Ukraine had fully earned its candidate status, though he cautioned that the accession process itself would be demanding.
Coalition of the Willing and G7 back US-led peace efforts
Sikorski also attended a meeting of the so-called Coalition of the Willing in Kyiv, where Polish Prime Minister Donald Tusk addressed leaders remotely.
British Prime Minister Keir Starmer and French President Emmanuel Macron co-chaired the gathering via video link.
In a joint statement, the group of more than 30 nations said "they welcomed US ongoing efforts on peace negotiations", but added the discussions "must involve all relevant parties".
They called on Russia to agree to a "full, unconditional ceasefire" and backed further sanctions, action against Russia's shadow fleet and disruption of its financial networks.
Also, world leaders from the G7, including US President Donald Trump, have reaffirmed their "unwavering support for Ukraine in defending its territorial integrity and right to exist, and its freedom, sovereignty and independence".
The countries expressed backing for Trump's efforts to bring both sides to direct talks and launch a peace process.
France currently holds the G7 presidency; the group also includes Japan, Canada, Germany, the United States, the United Kingdom and Italy.
European Parliament adopts resolution condemning Russia
Meanwhile, in Brussels, the European Parliament held an emergency plenary session to mark the anniversary.
Parliament President Roberta Metsola declared that the institution had not let Ukraine down over the past four years.
MEPs passed a resolution holding Russia and its allies, including Belarus, fully responsible for the war and its atrocities, and called for further sanctions on Moscow.
(ał)
Source: IAR, PAP