KYIV, Ukraine — Leaders from four major European countries threatened to ratchet up pressure on Russian President Vladimir Putin if he does not accept an unconditional 30-day ceasefire in Ukraine that they offered on Saturday in a strong show of unity with Kyiv.

The leaders of France, the United Kingdom, Germany and Poland said their proposal for a ceasefire to start on Monday was supported by U.S. President Donald Trump, whom they had briefed over the phone earlier in the day.

There was no immediate response from Moscow, whose own unilateral three-day ceasefire declared for the 80th anniversary of victory over Nazi Germany expires Saturday. Ukraine says Russian forces have repeatedly violated it. In March, the United States proposed an immediate, limited 30-day truce, which Ukraine accepted, but the Kremlin has held out for terms more to its liking.

Ukrainian President Volodymyr Zelenskyy, speaking to reporters alongside the European leaders in Kyiv, called their meeting “a very important signal.”

French President Emmanuel Macron said that the U.S. would take the lead in monitoring the proposed cease-fire, with support from European countries, and threatened “massive sanctions … prepared and coordinated, between Europeans and Americans,” should Russia violate the truce.

Macron traveled to Kyiv with British Prime Minister Keir Starmer, German Chancellor Friedrich Merz and Polish Prime Minister Donald Tusk.

“This is Europe stepping up, showing our solidarity with Ukraine,” Starmer said.

Retired Lt. Gen. Keith Kellogg, Trump’s special envoy to Ukraine and Russia, said Saturday that a “comprehensive” 30-day ceasefire, covering attacks from the air, land, sea and on infrastructure, “will start the process for ending the largest and longest war in Europe since World War II.”

Europe Threatens More Sanctions if Russia Ignores Ceasefire Offer

Progress on ending the three-year war has seemed elusive in the months since Trump returned to the White House, and his previous claims of imminent breakthroughs have failed to come to fruition. Trump has previously pushed Ukraine to cede territory to Russia to end the war, threatening to walk away if a deal becomes too difficult.

Since the start of U.S.-mediated talks, Russia has kept up attacks along the roughly 1,000-kilometer (600-mile) front line, including deadly strikes on residential areas with no obvious military targets.

The ceasefire would include a halt to fighting on land, sea and in the air. The European leaders threatened to ratchet up sanctions, including on Russia’s energy and banking sectors, if Putin did not comply.

The priority was to make it too costly for Russia to keep fighting in Ukraine, said Ukrainian Foreign Minister Andrii Sybiha.

When asked how the monitoring mechanism would work, Sybiha told The Associated Press the details were still being discussed.

Addressing scepticism over whether fresh sanctions against Moscow, which has so far managed to keep fighting in the war, Merz said “almost all member states of the European Union and a large coalition of the willing around the world are determined to enforce these sanctions even if our initiative of the weekend should fail.”

The leaders also discussed security guarantees for Ukraine.

Building up Kyiv’s military capabilities will be a key deterrent against Russia and require supplying Ukraine with robust quantities of arms to deter future attacks and investing in its defense sector. A force comprised of foreign troops could also be deployed as an added “reassurance” measure, Macron said.

He said details about potential European deployments to Ukraine were still being fine-tuned. No mention was made of NATO membership, still Kyiv’s top choice for a security guarantee.

Earlier on Saturday, the European leaders joined a ceremony at Kyiv’s Independence Square marking the 80th anniversary of the end of World War II. They lit candles alongside Zelenskyy at a makeshift flag memorial for fallen Ukrainian soldiers and civilians slain since Russia’s invasion.

Russian Attacks Continue

Russian shelling in Ukraine’s northern Sumy region over the past day killed three residents and wounded four more, local officials said. Another civilian died Saturday as a Russian drone struck the southern city of Kherson, according to regional Gov. Oleksandr Prokudin.

The U.S. Embassy in Kyiv on Friday warned of a “potentially significant” Russian air attack in the coming days, without giving details.

Russia in November gave the U.S. brief advance warning before striking Ukraine for the first time with its Oreshnik intermediate-range ballistic missile, an experimental hypersonic weapon that Putin claimed could travel at 10 times the speed of sound.

Ukrainian Telegram channels linked the embassy’s warning to reports of an imminent flight ban by Moscow over the Kapustin Yar military training and rocket launch complex. A similar flight ban preceded November’s strike. There was no immediate comment from Russian officials.

Trump said last week that he doubts Putin wants to end his war in Ukraine, expressing new skepticism that a peace deal can be reached soon, and hinted at further sanctions against Russia.

Ukraine’s European allies view its fate as fundamental to the continent’s security, and pressure is now mounting to find ways to support Kyiv militarily, regardless of whether Trump pulls out.

Associated Press writers Thomas Adamson in Paris, Philipp Reissfelder in Berlin and Danica Kirka in London contributed to this report.

Follow AP’s coverage of the war in Ukraine at https://apnews.com/hub/russia-ukraine