Russia, which launched its full-scale invasion of neighbouring Ukraine in February 2022, has dismissed the Lucerne event as a US-orchestrated plot.

It has repeatedly said it will not participate in any talks unless Kyiv accepts Russia's annexation of the roughly 20 percent of Ukraine's territory it currently occupies.

"Russia has not been invited at this stage," the foreign ministry in Bern said. "Switzerland has always shown openness to extending an invitation to Russia for this summit.

"However, Russia has said repeatedly and also publicly that it has no interest in participating in this first summit. The summit in Switzerland is intended to initiate a peace process.

"Switzerland is convinced that Russia must be involved in this process. A peace process without Russia is unthinkable."

For now, the attendance of Ukrainian President Volodymyr Zelensky and US President Joe Biden has not been confirmed.

Another big unknown is whether Moscow's key ally China will attend.

China has never condemned Russia's attack on Ukraine, and stands accused of indirectly supporting the war through its strategic partnership with its neighbour Moscow.

The weekend conference will be held on June 15-16 at the luxury Burgenstock resort near the central city of Lucerne.

The list of participating countries will be published shortly before the conference begins, but they include countries from every continent including members of the G7, the G20 and the BRICS group.

The G7 summit will be held in neighbouring Italy from June 13 to 15.

The Vatican, the European Union, the United Nations, the Council of Europe and the Organization for Security and Co-operation in Europe have also been invited.

Bern said the peace summit was expected to last just over a day.

"All states present at the summit should contribute their ideas and visions for a just and lasting peace in Ukraine," the foreign ministry said.

The talks aim to "promote a common understanding of a possible framework to reach this goal", and "jointly define a roadmap on how to involve both parties in a future peace process".

On the ground, Russia has made recent advances against Ukraine's outgunned, under-equipped forces, ahead of the long-awaited arrival of the bulk of US weapons to the front to support Kyiv's troops.