The leaders of Germany and France will try to convince Russia’s President Vladimir Putin to accept a new peace plan for Ukraine today, in a desperate search for a political solution to a war spiralling out of control on the European Union’s doorstep.

The surprise joint mission by Chancellor Angela Merkel and President François Hollande signals deep concerns in EU capitals that the escalation of fighting in Ukraine marks a dangerous new phase of a conflict which has damaged ties with Russia and had an adverse impact on some EU economies.

It also marks a widening gap in transatlantic approaches to Russia’s apparent backing of the separatists who have been waging an insurgency in eastern Ukraine for nearly a year. In Kiev, the US Secretary of State, John Kerry, warned that the US “cannot close [its] eyes to tanks that are crossing the border”, and underscored that the Obama administration was close to a decision on sending arms to the Ukrainian government.

EU leaders, mindful of their close economic and trade ties to Moscow, have been more cautious and made repeated attempts to broker ceasefires. The two leaders flew first to Kiev today to seek the Ukrainian president’s support for the plan, before flying to Moscow for talks with the Russian leader on Friday.

Ukraine crisis: A timeline of the conflict Show all 23 1 /23 Ukraine crisis: A timeline of the conflict Ukraine crisis: A timeline of the conflict 30 November 2013 Public support grows for the “Euromaidan” anti-government protesters in Kiev demonstrating against Yanukovych’s refusal to sign the EU Association Agreement as images of them injured by police crackdown spread. EPA Ukraine crisis: A timeline of the conflict 20 February 2014 Kiev sees its worst day of violence for almost 70 years as at least 88 people are killed in 48 hours, with uniformed snipers shooting at protesters from rooftops. AFP/Getty Images Ukraine crisis: A timeline of the conflict 22 February 2014 Yanukovych flees the country after protest leaders and politicians agree to form a new government and hold elections. The imprisoned former Prime Minister, Yulia Tymoshenko, is freed from prison and protesters take control of Presidential administration buildings, including Mr Yanukovych's residence. Genya Savilov/AFP/Getty Imageses Ukraine crisis: A timeline of the conflict 27 February 2014 Pro-Russian militias seize government buildings in Crimea and the new Ukrainian government vows to prevent the country breaking up as the Crimean Parliament sets a referendum on secession from Ukraine in May. Sean Gallup/Getty Images Ukraine crisis: A timeline of the conflict 16 March 2014 Crimea votes overwhelmingly to secede from Ukraine and join Russia in a ballot condemned by the US and Europe as illegal. Russian troops had moved into the peninsula weeks before after pro-Russian separatists occupied buildings. EPA Ukraine crisis: A timeline of the conflict 6 April 2014 Pro-Russian rebels seize government buildings in the eastern cities of Donetsk, Luhansk and Kharkiv, calling for a referendum on independence and claiming independent republic. Ukraine authorities regain control of Kharkiv buildings on 8 April after launching an “anti-terror operation” but the rest remain out of their control. EPA/PHOTOMIG Ukraine crisis: A timeline of the conflict 7 June 2014 Petro Poroshenko is sworn in as Ukraine's president, calling on separatists to lay down their arms and end the fighting and later orders the creation of humanitarian corridors, since violated, to allow civilians to flee war zones. Getty Images Ukraine crisis: A timeline of the conflict 27 June 2014 The EU signs an association agreement with Ukraine, along with Georgia and Moldova, eight months after protests over the abandonment of the deal sparked the crisis. LOUISA GOULIAMAKI/AFP/Getty Images Ukraine crisis: A timeline of the conflict 17 July 2014 Malaysian Airlines flight MH17 is shot down over eastern Ukraine, killing all 298 people on board. Ukrainian intelligence officials claim it was hit by rebels using a Buk surface-to-air launcher in an apparent accident. Ukraine crisis: A timeline of the conflict 22 August 2014 A Russian aid convoy of more than 100 lorries enters eastern Ukraine and makes drop in rebel-controlled Luhansk without Government permission, sparking allegations of a “direct violation of international law”. Reuters/Alexander Demianchuk Ukraine crisis: A timeline of the conflict 29 August 2014 Nato releases satellite images appearing to show Russian soldiers, artillery and armoured vehicles engaged in military operations in eastern Ukraine. Nato Ukraine crisis: A timeline of the conflict 8 September 2014 Russia warns that it could block flights through its airspace if the EU goes ahead with new sanctions over the ongoing crisis and conflict EPA Ukraine crisis: A timeline of the conflict 17 September 2014 Despite the cease-fire and a law passed by the Ukrainian parliament on Tuesday granting greater autonomy to rebel-held parts of the east, civilian casualties continued to rise, adding to the estimated 3,000 people killed Reuters Ukraine crisis: A timeline of the conflict 20 October 2014 A 'tactical missile' explosion at a factory sends blast wave across rebel-held cityof Donetsk YouTube Ukraine crisis: A timeline of the conflict 16 November 2014 The fragile ceasefire gives way to an increased wave of military activity as artillery fire continues to rock the eastern Ukraine's pro-Russian rebel bastion of Donetsk Getty Ukraine crisis: A timeline of the conflict 26 December 2014 A new round of ceasefire talks, scheduled on neutral ground in the Belariusian capital Minsk, are called off AFP/Getty Ukraine crisis: A timeline of the conflict 12 January 2015 Soldiers in Debaltseve were forced to prepare heavy defences around the city; despite a brief respite to the fighting in eastern Ukraine, hostilities in Donetsk resumed at a level not seen since September 2014 AFP/Getty Ukraine crisis: A timeline of the conflict 21 January 2015 13 people are killed during shelling of bus in the rebel-held city of Donetsk Reuters Ukraine crisis: A timeline of the conflict 24 January 2015 Ten people were killed after pro-Russian separatists bombarded the east Ukrainian port city of Mariupol AP Ukraine crisis: A timeline of the conflict 2 February 2015 There was a dangerous shift in tempo as rebels bolstered troop numbers against government forces AFP/Getty Ukraine crisis: A timeline of the conflict 11 February 2015 European leaders meet in Minsk and agree on a ceasefire in eastern Ukraine beginning on February 14. From left to right: Belarus President Alexander Lukashenko, Russian President Vladimir Putin, German Chancellor Angela Merkel, France's President Francois Hollande and Ukrainian President Petro Poroshenko. MAXIM MALINOVSKY | AFP | Getty Images Ukraine crisis: A timeline of the conflict 13 February 2015 Pro-Russian rebels in the city of Gorlivka, in the Donetsk region, fire missiles at Ukrainian forces in Debaltseve. Fighting continued in Debaltseve for a number of days after the Minsk ceasefire began. ANDREY BORODULIN | AFP | Getty Images Ukraine crisis: A timeline of the conflict 18 February 2015 Ukrainian soldiers repair the bullet-shattered windshield of their truck as their withdraw from the strategic town of Debaltseve. Following intense shelling from pro-Russian rebels, Ukrainian forces began to leave the town in the early hours of February 18. Brendan Hoffman | Getty Images

Mr Hollande said the Franco-German plan would be based on the “territorial integrity” of Ukraine and would require a lasting ceasefire. It is understood to be based on a nine-point plan originally presented by Mr Putin, which Ms Merkel and Mr Hollande have adapted to include points raised in other peace plans, such as more autonomy for some eastern areas.

It is also believed to include recognition of language rights for Russian speakers in the whole of Ukraine; recognition of Kiev’s overall authority by the rebels; and Russian acceptance of a monitoring force to prevent further movement of troops or weapons across the border from Russia.

Mr Hollande said that France was “opposed to Ukraine joining Nato”, one of Russia’s fears, and some guarantee along those lines may also be part of the plan.

The latest initiative by the EU’s foreign policy heavyweights comes after a peace plan agreed in Minsk, the Belarus capital, last September fell apart. A tenuous ceasefire held for a while but in recent weeks rebels have resumed their offensive and dozens of civilians have been killed.

“In Ukraine it is now war,” Mr Hollande said. “Heavy weapons are being used. Civilians are dying. No one will be able to say that France and Germany didn’t try everything possible [to stop the fighting].”

Western nations were confronted with two options, he said: arming the Ukrainians to help them confront the “separatists armed by Moscow” or making a final attempt at diplomacy.

French President Francois Hollande is to propose a peace deal on Ukraine with Germany's Angela Merkel (EPA) (EPA/PHILIPPE WOJAZER / POOL MAXPPP OUT)

Mr Hollande made clear, however, that there would be further consequences for Russia if it did not commit to a new solution to end the war in Ukraine, which has killed more than 5,000 people. Negotiations “cannot go on indefinitely”, he warned.

Both France and Germany have long-standing trade ties with Moscow. While this has made them more cautious about imposing economic sanctions against Russia, it does give them more clout with Mr Putin.

Moscow welcomed the initiative, with Mr Putin’s adviser Yuri Ushakov saying Russia was “ready for a constructive conversation”. Russia denies that it is arming the rebels or sending troops to eastern Ukraine, despite a dossier of Nato evidence.

Previous peace plans have apparently been agreed by Moscow, only for it to resume combative rhetoric within weeks. EU sanctions have hit Russia’s economy, but they have also had knock-on effects in the EU itself.

The US has taken a harder line, with Ashton Carter, the new nominee for Defence Secretary, telling Congress this week that “we need to support the Ukrainians in defending themselves”. Most European leaders are against this.

The German Defence Minister, Ursula von der Leyen, said at a Nato meeting in Brussels that it was necessary to “find a solution at the table and not on the [battle]field, because to give input to a potential escalation is not a good solution”.

The US is not involved in the new peace initiative and Mr Kerry has no plans to travel to Moscow. In Kiev, he repeated calls for Russia to back up words with actions. “We want a diplomatic solution but we cannot close our eyes to tanks crossing the border from Russia…into Ukraine,” he said.

“We cannot close our eyes to Russian fighters in unmarked uniforms crossing the border, and leading individual companies of so-called separatists in battle.”