Ukrainian President Volodymyr Zelenskiy said on Tuesday that the island state of Cape Verde had become the first African country to agree to attend a world "peace summit" aimed at finding a solution to Ukraine's more than two-year-old war against Russia.

The summit, to which Russia has not been invited, is to take place in Switzerland on June 15-16, and Ukraine hopes to marshal broad support to persuade Moscow to agree to terms that Kyiv deems acceptable.

Ukraine has been deploying great efforts to bring countries from the Global South onside, though Russia benefits from longstanding ties with Moscow from Soviet times.

In a post on the Telegram messaging app, Zelenskiy said he thanked Cape Verde Prime Minister Ulisses Correia e Silva during a telephone conversation.

"I thanked him for his support for the peace formula and his personal principled position on the Russia invasion," Zelenskiy wrote. "Cape Verde is the first African country to confirm its participation in the peace summit."

The president, who made a brief stopover in Cape Verde last year on his way to Argentina, also mentioned the conversation in his nightly address as a step in organising the June gathering.

"Every continent will be represented at our summit in Switzerland, different nations, small or large, those who have clearly shown their support for international law and those who will do so," he said.

Zelenskiy stands by a peace plan calling for the withdrawal of Russian troops, the restoration of Ukraine's post-Soviet borders and a process to bring Russia to account for its actions. He hopes more than 80 countries will attend.

Russia says the plan takes no account of "new realities" in Ukraine and dismisses the summit as meaningless if Moscow is not a party.

The Swiss government said last week that a peace process without Russia "is not possible." The aim of the meeting, it said, was "to inspire a future peace process." REUTERS