World leaders on Sunday backed Ukraine's independence and territorial integrity, and the need for eventual talks with Russia on ending the war -- but left the key questions of how and when unresolved.

More than two years after Russia invaded, leaders and top officials from more than 90 states spent the weekend at a Swiss mountainside resort for a two-day summit dedicated to resolving the largest European conflict since World War II.

Ukrainian President Volodymyr Zelensky hailed the diplomatic "success" of the event, which took place without Russia, and said the path was open for a second peace summit, with a view to ending the war with a just and lasting settlement.

But he told a closing press conference that "Russia and their leadership are not ready for a just peace".

"Russia can start negotiations with us even tomorrow without waiting for anything -- if they leave our legal territories," he said.

Moscow meanwhile doubled down on its demand for Kyiv's effective surrender as a starting point for negotiations.

- Sovereignty and independence -

"Reaching peace requires the involvement of and dialogue between all parties," said the summit's final communique, supported by the vast majority of countries that attended the summit at the Burgenstock complex overlooking Lake Lucerne.

The document also reaffirmed a commitment to the "sovereignty, independence and territorial integrity of all states, including Ukraine, within their internationally recognised borders".

It said any threat or use of nuclear weapons in the war was "inadmissible", and food security "must not be weaponised".

The declaration also urged a full exchange of prisoners of war and the return to Ukraine of "all deported and unlawfully displaced children", and other unlawfully detained Ukrainian civilians.

But not all attendees backed the joint communique, with India, Saudi Arabia and the United Arab Emirates among those who did not appear on a list of states backing it.

Though the declaration committed countries to taking "concrete steps" in future to "further engagement of the representatives of all parties", the way to bring Russia into the process remained unclear.

Swiss President Viola Amherd, hosting the summit, admitted "the road ahead is long and challenging."

Kremlin reiterates Putin call

The summit, snubbed by Russia and its ally China, came at a point when outmanned and outgunned Ukraine is struggling on the battlefield.

Zelensky said the current level of Western military aid being sent to his country was not enough to ensure Kyiv wins the war.

"There is aid. There are serious packages. Is it enough to win? No. Is it late? Yes," he told reporters.

On Friday, Putin demanded Kyiv's effective surrender as a basis for peace talks, but his call for Ukraine to withdraw its troops from the south and east of the country, which Russia claims to have annexed, was widely dismissed at the summit.

The Kremlin nonetheless insisted Sunday that Ukraine should "reflect" on Putin's demands, citing the military situation on the ground.

"The current dynamic of the situation at the front shows us clearly that it's continuing to worsen for the Ukrainians," Kremlin spokesman Dmitry Peskov said. 

"It's probable that a politician who puts the interests of his country above his own and those of his masters would reflect on such a proposal."

Russia on Sunday claimed its troops had captured Zagrine village in southern Ukraine, continuing its progress on the front line.

- Children, nuclear fears -

The Burgenstock talks were framed around areas of common ground between Zelensky's 10-point peace plan presented in late 2022, and a 2023 UN resolution on the war that passed with the support of 141 countries.

Switzerland set a tight remit in an attempt to garner the broadest support by sticking firmly to topics covered by international law and the United Nations Charter -- and from there, sketch out a framework towards a lasting peace.

The summit focused Sunday on food security and freedom of navigation on the Black Sea; nuclear safety and security to curb the risk of a disaster; and humanitarian issues including the return of deported children or the welfare of POWs.

Standing beside Zelensky, Chilean President Gabriel Boric told the closing press conference that the summit was not about NATO, left or right political convictions, or North versus South debates.

"This is about respect of international law and human rights as foundational principles of our living together. And this is applicable in Ukraine, in Gaza and in every other conflict in the world," he said.

"We aspire that Russia and Ukraine soon engage in dialogue, with respect of territorial integrity of Ukraine," he added.

Ghana's President Nana Akufo-Addo stressed the war's impact on food exports from Ukraine and how the war had sent inflation soaring, harming living standards in some of the world's poorest countries.

"The consequences of the invasion go far beyond the confines of Europe. Indeed in many ways, Africa has been the greatest victim," he said.

Akufo-Addo said a method should be found whereby Russia and China join in the talks process, "if we're ever going to arrive at a definitive settlement".

Zelensky called for Beijing, which refused to send a delegation to the summit due to Russia's absence, to engage seriously with the developing peace proposals.

"China could help us," Zelensky told reporters, adding that though it has close ties with the Kremlin, "Ukraine never said that China is our enemy". 

"I always say that Ukraine has only one enemy: Putin."