Ukraine's leader is visiting Brussels, having urged the leaders of France, Germany and the UK to provide fighter jets for the war against Russia.
"Europe will always remain free as long as we are together," Volodymyr Zelensky told the European Parliament.
He was also due to attend a summit of EU leaders, on his second trip abroad since the war began.
Ahead of the meeting, several leaders stressed that a decision on warplanes would be a collective move.
Poland's prime minister said his country could only act "within the entire formation of Nato", while Dutch Prime Minister Mark Rutte said the issue had to be discussed behind closed doors.
The Kremlin warned on Thursday that the line between direct and indirect Western involvement in the conflict was disappearing.
Mr Zelensky was given a standing ovation at the European Parliament, where President Roberta Metsola called on EU states to consider quickly Kyiv's request for the jets Ukraine needed.
In his speech, Mr Zelensky repeatedly linked Ukraine to a European way of life. Ukraine has applied to join the EU and is urging the bloc's leaders to throw its weight behind a swift course to accession, which usually takes many years.
"Ukraine is going to be a member of the European Union," he told MEPs. Together with Europe, he said Ukrainians were defending themselves against the "biggest anti-European force of the modern world".
The Ukrainian leader had earlier travelled from Paris with France's Emmanuel Macron, where he had also held talks with Germany's Olaf Scholz. Before visiting Paris he had been assured by UK Prime Minister Rishi Sunak that nothing was off the table.
Mr Zelensky said Germany and France had the potential to be "game-changers" in the war. The sooner Ukraine received heavy, long-range weapons and modern planes, "the quicker this Russian aggression will end", he explained.
Although President Macron has previously signalled some openness to providing fighter jets - Mr Scholz has not.
The French leader vowed Ukraine could count on his support, with France "determined to help Ukraine to victory and the re-establishment of its legitimate rights". Chancellor Scholz added: "The position is unchanged: Russia must not win this war."
Because of the 11-month long Russian invasion, Mr Zelensky rarely leaves his own country and a senior Ukrainian official said that the purpose of his trip was to obtain results.
However, Thursday's EU leaders' summit is not a forum for weapons pledges but a chance for Ukraine's president to be in the room with all 27 EU leaders.
He argues fighter jets and long-range missiles are important in addition to the Leopard 2 tanks that Western nations have recently committed to supplying. While Mr Zelensky said he had discussed the issue of combat planes in Paris, he warned there was "very little time" to provide much-needed weaponry.
Dutch Prime Minister Mark Rutte said that many sensitive issues had to be discussed before a decision could be made on supplying fighter jets. "The pros and cons - you have to make absolutely sure that you are not getting into an Article Five direct confrontation between Nato and Russia," he told the BBC.
Asked by reporters in Moscow about the growing debate over sending warplanes to Ukraine, Kremlin spokesman Dmitry Peskov said Russia saw it as evidence of the growing involvement of the UK, France and Germany in the conflict.
"We regret this and state that such actions of these countries lead to the escalation of tension around this conflict, prolong it and make it more painful and torturous for Ukraine," said Mr Peskov.
Moscow has repeatably warned the West against weapons deliveries since the war began, frequently threatening to retaliate against what it calls "provocations".
Chancellor Scholz agreed only recently to allow German Leopard tanks and President Zelensky has previously expressed frustration with Mr Macron, who continued to hold phone calls with Russian President Vladimir Putin after the invasion.
But the Ukrainian president told French newspaper Le Figaro he believed Mr Macron had changed and said the fact he had "opened the door" to tank deliveries last month showed this.
Mr Zelensky had earlier addressed a joint session of the UK Parliament in Westminster Hall, underlining his plea for fighter jets: "Freedom will win - we know Russia will lose."
Downing Street said UK Defence Secretary Ben Wallace was investigating what aircraft could potentially be offered, but emphasised this was "a long-term solution" and that training pilots could take years.