This evening's gathering was due to involve leaders from Germany, Poland, Italy, Denmark, The Netherlands and the European Union's main institutions.

French President Emmanuel Macron and British premier Keir Starmer were set to miss it due to schedule clashes, but were sending their foreign ministers instead.

The huddle comes just over a month before Trump moves into the White House, having pledged to bring a swift end to a conflict that NATO says has left more than one dead million and wounded since Russia's 2022 invasion.

There are fears that Trump could pull US support for Kyiv and force it to make painful concessions to Moscow. European leaders, keen not to be left on the sidelines, are scrambling to come up with their own plans.

"Europe needs a strong, united position to ensure lasting peace," Zelensky posted on X as he arrived in the Belgian capital.

- 'Position of strength' -

European leaders insist that only Ukraine should decide when it is ready to negotiate with Russia.

German Chancellor Olaf Scholz told reporters upon arrival in Brussels the priority was to secure the "sovereignty of Ukraine -- and that it will not be forced to submit to a dictated peace."

But discussions have begun between some capitals over the potential deployment of European troops to Ukraine to secure any eventual ceasefire.

While this was raised at a recent meeting between Macron and Polish Prime Minister Donald Tusk, diplomats say it remains too early to draw up concrete proposals.

Scholz told reporters that discussing boots on the ground was premature, saying it "does not make sense" at this stage.

Rutte instead said Kyiv's allies should focus on ramping up arms supplies -- and urged them not to debate possible peace conditions in public as it risks playing into Moscow's hands.

"What we should focus on now is making sure that Ukraine gets to a position of strength," he said.

"If we now start to discuss amongst ourselves what a deal could look like, we make it so easy for the Russians."

Western backers are seeking to shore up Ukraine's forces as Kyiv's fatigued troops are losing ground across the frontline and Moscow has deployed North Koreans to the battlefield.

Zelensky said the leaders in Brussels would discuss "how to urgently strengthen Ukraine on the battlefield, politically and geopolitically". He will also attend a summit with his 27 EU counterparts on Thursday.

- Air defence -

Most immediately Zelensky is pleading for over a dozen more air defence systems to try to help stave off his Russian barrages against Ukraine's power grid.

But Ukraine's leader has said Trump's arrival could mean the war ends next year, and has called for allies to help secure a peace deal that Moscow cannot violate.

As the change of guard approached in the US, Zelensky has appeared to soften his stance on any potential peace push.

He has said that if Ukraine is given firm security guarantees by NATO and enough weaponry it could agree to a ceasefire along current lines and look to regain the rest of its territory through diplomatic means.

But NATO members have rebuffed Kyiv's calls for an invitation to join their alliance right away, sparking speculation that sending peacekeepers could be an alternative.

"Officially that is not on the agenda, but since there will be a lot of important people in the same room, it cannot entirely be ruled out," a NATO diplomat said.

The meeting "will be basically about Zelensky asking for more military aid", the diplomat added.