The 30 countries in the "coalition of the willing" supporting Kyiv will hold a video call on Tuesday following talks in Geneva on the US plan for Ukraine, French President Emmanuel Macron said.
"We will hold a meeting Tuesday afternoon to coordinate on this point, and to see what progress will be made in the Geneva negotiations in coming days, and to be able to take new initiatives," he told reporters on the sidelines of a G20 summit in Johannesburg.
Mr Macron said that Russia would "betray" its promise and "come back" if the Ukraine were forced to reduce its army, as proposed under a US plan.
European leaders meeting at a G20 summit in South Africa have pushed back at the unilateral plan by US President Donald Trump that aims at ending the war in Ukraine on terms favouring Russia.
"We know that if there are no elements of deterrence, the Russians will come back and break their promises," Mr Macron told journalists.
National security advisers from France, Britain and Germany will meet European Union, US and Ukrainian officials in Geneva tomorrow to discuss Washington's proposed peace plan for Ukraine, officials said on the sidelines of the G20 summit.
France, Britain and Germany have an informal security alliance called the E3.
A US official said US Army Secretary Daniel Driscoll had already landed in Geneva for the talks and a Ukrainian delegation will arrive tonight.
US Special Envoy Steve Witkoff and Secretary of State Marco Rubio are due to arrive tomorrow.
A German government source added that a European draft peace plan, which is based on the US proposal, had been sent to Ukraine and to the US administration.
Earlier, Taoiseach Micheál Martin told the G20 summit in Johannesburg that "there must be renewed efforts to end the illegal invasion of Ukraine by Russia" and the war that has ensued.
He was speaking as US President Donald Trump urged Ukraine to accept his administration's plan aimed at ending the war with Russia by ceding territory.
Addressing the summit as a guest of the South African presidency of the G20, Mr Martin said that "we must work very hard" to end the wars in Ukraine, Gaza and Sudan.
In his speech, the Taoiseach also underlined Ireland's commitment to multilateralism.
He said Ireland, along with the European Union, was "committed to an open and most based multilateral trading system with the modernised WTO (World Trade Organisation) at its core".
Watch: Why is the United States boycotting the G20 summit?
Mr Martin said the rules and the standards that the WTO provides were "crucial for all of us who depend on global trade and allow all trading nations to benefit the stability and predictability provided by the rules-based multilateral trading system is key in supporting sustainable development".
He also said Ireland was supportive of the institutions and initiatives that assist countries with debt issues.
"These include the G20 which is developed and is overseeing the implementation of the common framework for debt treatments, the global sovereign debt roundtable and the Paris Club, and we continue to call where appropriate reform and improvements of these institutions and initiatives," he said.
"These priorities have guided our active engagement in the G20 this year," he told the summit, "and we support South Africa in this endeavour."
In a news conference on the eve of the summit in Johannesburg, UN Secretary-General António Guterres picked up the theme of equality.
"Africa has been a double victim of colonialism," he told reporters, "first, through centuries of exploitation and plunder and then again when international institutions were created - when most African countries were still under colonial rule, and their voices were absent from the table."
"Today, Africa remains woefully under-represented across global institutions," he said, adding: "This must change."
But themes like these have drawn the ire of Washington over the year of G20 working group meetings, which, along with US President Donald Trump’s claims of persecution of white South Africans, culminated in a full boycott.
Early this year, US Secretary of State Marco Rubio said South Africa’s slogan was "anti-American".
And it is not the only thing upsetting the White House.
The G20’s heavy focus on the scaling up of renewable energy directly challenges the US president’s contention that climate change is a hoax and his promise to "drill, baby, drill" for more fossil fuel.
Johannesburg airport is decorated with posters declaring: "Africa and Europe team up for clean energy".
And yesterday, President of the European Commission Ursula von der Leyen announced a pledge of €7 billion to boost renewable energy generation and electricity access across Africa.
"We are turbo-charging Africa’s clean-energy transition," she told a Global Citizen event, adding "millions more people could gain access to electricity".
Mr Martin also underlined Ireland’s commitment to scaling up renewable energy, telling the event: "We are very windy in Ireland".
The absence of the US means there is no pushback in real time.
But the stark divide between America’s world view and the one being embraced in Johannesburg does raise the question of whether any of this year’s G20 agenda will survive into the US presidency, due to begin on 1 December.
Additional reporting: AFP
