Ukrainian President Volodymyr Zelensky on Thursday signed a 10-year security pact with the European Union in Brussels, the latest deal aimed at shoring up long-term support for Kyiv in its fight with Russia.

Days after the EU said it was opening formal membership negotiations with Kyiv, Zelensky attended a summit of EU leaders to meet with some of Ukraine's staunchest supporters in the face of the Russian invasion.

"Thanks to you and to all the leaders of the EU for such historical outcome. We waited for this a long period of time," Zelensky told reporters in Brussels.

He however pointed to the need to take the "next steps" including on air defence. "We need them urgently on the battlefield."

The security agreement being signed with the EU mirrors accords already struck by Kyiv with a raft of countries, including EU heavyweights Germany and France.

"For the first time, this agreement will enshrine the commitment of all 27 Member States to provide Ukraine with extensive support, regardless of any internal institutional changes," he said in a post on X.

"Each step we take brings us closer to our historic goal of peace and prosperity in our common European home," Zelensky said.

EU chief Charles Michel hailed the "positive" agreements.

"It's very important so that we can give the message that we intend to support Ukraine for as long as it takes," Michel said, standing next to Zelensky.

Ukraine has signed 17 similar bilateral security agreements, including with the United States, Britain and Japan.

They are not mutual defence pacts, but instead outline key countries' plans to support Ukraine with military, financial, humanitarian and political aid over a number of years.

The pact, made public shortly after it was signed, said the EU would look to continue financing weapons deliveries for Ukraine, keep training Kyiv's troops, and step up efforts to bolster the country's defence industry.

But there were no concrete commitments of new aid from the EU, after some countries refused to make any pledge too definite.

Instead, the accord says only that further annual tranches of support worth around the same as a five-billion-euro package for this year "could be envisaged" until 2027.

As with the other pacts, it also includes a clause saying the EU would consult with Ukraine within 24 hours in case of a "future aggression" by Russia.

Ukraine has portrayed the agreements as a bridge towards membership in the EU and NATO.

The initiative to sign them was announced at NATO's summit last year to appease Kyiv after it was refused a clear timeframe for joining the alliance.

© Agence France-Presse