"We must continue to strengthen the partnership between NATO and the European Union. And we must further strengthen our support to Ukraine," NATO chief Jens Stoltenberg said after signing a joint declaration with the EU's top officials.

Countries in NATO and the EU -- which share 21 members -- have funnelled billions of dollars of arms to Kyiv that have helped it push back Moscow's forces.

The United States, Germany and France have announced they will now also supply Ukraine with armoured fighting vehicles -- but Kyiv has pleaded for modern heavy tanks to be sent as well.

"I think that Ukraine should get all the necessary military equipment they need and they can handle to defend the homeland," European Commission President Ursula von der Leyen said.

"This means of course, advanced air defence systems, but also other types of advanced military equipment, as long as it is necessary to defend Ukraine."

Stoltenberg said Kyiv's Western backers will meet next week with Ukraine's defence minister "to discuss exactly what types of weapons are needed and how can allies provide those weapons".

"This is not only about adding more systems, more platforms, more weapons, but also ensuring that the platforms, the weapons we have already provided are working as they should," he said.

Moscow's attack on Ukraine has upended the European security order and spurred calls for the EU and NATO to work more closely together to protect the continent.

The two organisations agreed that NATO, backed by the military might of the United States, remains the bedrock for Europe's security despite attempts by the EU to boost its role in defence.

"Our declaration makes clear that NATO remains the foundation of collective defence and remains essential for Euro-Atlantic security," Stoltenberg said.

"It also recognises the value of a more capable European defence that contributes positively to our security and is complementary to and interoperable with NATO."