World leaders headed to Switzerland on Saturday for a first summit on peace in Ukraine, after Vladimir Putin demanded Kyiv effectively surrender if it ultimately wants negotiations with Moscow.

The two-day gathering at the luxury Burgenstock resort brings together Ukrainian President Volodymyr Zelensky and more than 50 other heads of state and government, but without Russia taking part.

Switzerland says the aim is to lay the early groundwork for a path to peace eventually involving Moscow, but Russian President Vladimir Putin on Friday branded the summit a "trick to distract everyone".

He said Moscow, which launched its full-scale invasion of Ukraine in February 2022, would cease fire and begin peace talks "immediately" if Kyiv pulled its troops out of the east and south and gave up its NATO membership bid.

Zelensky slammed Putin's demands as a territorial "ultimatum" reminiscent of Nazi Germany's dictator Adolf Hitler, while NATO and the United States also immediately rejected the hardline conditions.

After almost a year of stalemate, Ukraine was forced to abandon dozens of frontline settlements this spring, with Russian troops holding a significant advantage in manpower and resources.

But since mid-May, Russian progress has slowed and Zelensky hopes to swing the momentum further with the back-to-back G7 and peace summits.

- G7 $50 bn, security deal -

The G7 summit in Italy, which Zelensky attended, offered on Thursday a new $50 billion loan for Ukraine, using profits from the interest on frozen Russian assets.

Leaders of the Group of Seven rich democracies said they would support Ukraine "for as long as it takes".

Zelensky said the new loan would go towards "both defence and reconstruction", while Putin branded the move as "theft", warning it would "not go unpunished".

Meanwhile, a landmark 10-year security deal signed by Zelensky and US President Joe Biden on Thursday will see the United States provide Ukraine with military aid and training, with Zelensky calling it a bridge to joining the NATO defence alliance.

Biden will not go from Italy to Switzerland, sending instead his Vice President Kamala Harris, while the other G7 leaders from Britain, Canada, France, Germany, Japan and Italy are due to attend.

The EU chiefs and the presidents of Argentina, Colombia, Chile, Finland and Poland are among the others heading to Switzerland.

The Summit on Peace in Ukraine aims to see the 92 attending countries agree a final declaration on some tentative basic principles.

Russia's BRICS allies Brazil and South Africa are only sending an envoy, and India will be represented at the ministerial level, while China will not take part at all without Moscow's presence.

- Finding common ground -

The summit is being held at the ultra-exclusive Burgenstock hotel complex perched high above Lake Lucerne in classic picture-postcard Swiss scenery.

The gathering will focus on narrow themes, based on common ground between Zelensky's 10-point peace plan presented in late 2022, and UN resolutions on the war that passed with widespread support.

The summit aims to find paths towards a lasting peace for Ukraine, based on international law and the United Nations Charter; a possible framework to achieve this goal; and a roadmap as to how both parties could come together in a future peace process.

Experts have warned against too-high expectations from the gathering.

"Meaningful negotiations that could truly end the devastating war in Ukraine remain out of reach, as both Kyiv and Moscow stick to theories of victory that amount to outlasting the other," the International Crisis Group think tank said.

"Kyiv and its backers will be hard pressed to get tangible results from the meeting... beyond reaffirmations of the UN Charter's principles of territorial integrity."

- Nuclear, food, humanitarian focus -

A plenary session involving all delegations will be held on Saturday.

On Sunday, three topics will be discussed in detail in working groups: nuclear safety, freedom of navigation and food security, and humanitarian aspects. These will look at Black Sea shipping, prisoners of war, civilian detainees and deported children.

A second summit is envisaged, and Zelensky's chief of staff Andriy Yermak said Tuesday that Kyiv hoped Russia would attend and receive a "joint plan" presented by the other attendees.

The Burgenstock mountain is surrounded by the lake on three sides and the hotel complex is on a ridge some 450 metres above the water, making it relatively easy to seal off from traditional physical threats.

However, the Swiss government said its websites have been repeatedly hit with cyberattacks in the build-up to the summit, and has noted a surge in misinformation.

Samuel Charap, a Russia expert at the RAND think tank, said of the Swiss summit: "Russia is clearly going out of its way to demonstrate its pique with it... that tells you something.

"Avoiding the expansion of the pro-Ukraine coalition: they're concerned about this," he told AFP.