A crucial deal on Ukrainian grain exports that will collapse next week if Russia does not agree to renew it will top UN-EU talks happening outside Brussels on Thursday, EU chief Ursula von der Leyen said.

"The ball is in President (Vladimir) Putin's court" on whether to extend the so-called Black Sea grain deal beyond its expiry on Monday, she said, standing next to UN Secretary General Antonio Guterres.

Guterres said the UN's partnership with the EU on this and other issues was essential to "rebuilding trust with the developing world... and we don't have a moment to lose".

"This is when multilateralism is more vital than ever -- to bring peace, to protect the planet, to end hunger," he said.

The UN's Black Sea Grain Initiative, first struck in July 2022, expires on Monday unless Putin agrees to extend it -- something he has thus far held off saying he would do.

For Moscow, the fate of the agreement is a point of leverage as it pursues its war in Ukraine.

The deal, which Turkish President Recep Tayyip Erdogan helped broker, has allowed Ukraine to ship more than 32 million tonnes of grain past Russian warships in the Black Sea.

Much of the grain has gone to feed developing countries in Africa, the Middle East and elsewhere. If the exports were again blocked, food prices could spiral even higher than they are now.

Von der Leyen said the grain issue was "the big topic" on the table for the EU and UN teams as they held their annual high-level dialogue in the form of a two-day retreat in the town of La Hulpe, just south of Brussels.

The EU has organised complementary overland "solidarity lanes" that transport Ukrainian grain into the bloc on its way to other destinations. But the volume is a fraction of what grain freighters can take by sea.

Von der Leyen hailed Guterres's "tireless efforts to prolong the Black Sea Grain Initiative," saying "Russia has a responsibility to prolong it otherwise global food insecurity will be the consequence".

Other issues to be discussed in the EU-UN meeting were Russia's war in Ukraine, efforts to combat climate change, and developments in the digital economy, especially the need for international "guardrails" on artificial intelligence, von der Leyen and Guterres said. (AFP)