David Cameron and other world leaders have headed to France to warn the Russian President that he must seize the opportunity of elections in Ukraine and stem separatist violence gripping the country, offering him a choice of a cautious rapprochement or deeper sanctions.
Russia's President Vladimir Putin was due to meet with Mr Cameron and his French and German counterparts, who came straight from a G7 meeting in Brussels carrying a message that Moscow had a month to reverse its course in Ukraine and engage with its new leader.
They made clear that the election last month of Petro Poroshenko, a billionaire confectionery magnate, could prove a turning point in the future of Ukraine given his willingness to reach out to both Russian speakers in the restive east and to leaders in Moscow.
Ukraine has been gripped by turmoil since pro-EU protesters ousted Kremlin ally Viktor Yanukovych in February, prompting Moscow's annexation of Crimea and pro-Russian insurgencies in key cities in the east - unrest that US and EU leaders say the Kremlin is orchestrating.
“There is an opportunity for diplomacy to play a role and to chart a path because we've had these elections,” Mr Cameron said, adding that first Mr Putin must meet certain conditions laid down by the G7 leaders in a meeting which pointedly excluded Russia.
“President Putin must recognise the legitimate election of President Poroshenko. He must stop arms crossing the border into Ukraine. He must cease Russian support for separatist groups,” he said. “If these things don't happen, then sectoral sanctions will follow.
“The next month will be vital in judging if President Putin has taken these steps, and that is what I will urge President Putin to do.”
The US President, Barack Obama, was also travelling to Paris, and will join 17 other world leaders on the beaches of Normandy for commemorations marking the 70th anniversary of the D-Day landings. Unlike the Europeans, Mr Obama has decided not to hold official talks with Mr Putin, but said that should they bump into one another he will deliver a similar message.
“We are at a point where Mr Putin has a chance to get back into a lane of international law,” Mr Obama said, reiterating the demands of the G7 leaders. “If Mr Putin takes those steps then it is possible for us to begin to rebuild trust between Russia and its neighbours and Europe. Should he fail to do so there are going to be additional consequences.”
Whether Mr Putin will be receptive to these overtures is unclear. In an interview with French media ahead of travelling to Paris, he sent mixed signals to his critics. The Russian President repeated accusations that it was the EU and US who caused the crisis in Ukraine by backing the protesters who toppled ex-president Yanukovych. But he also hinted that talks with Mr Obama and Mr Poroshenko - a late addition to the guest list - could be on the cards.
“You know, I don't plan to evade anyone,” he told French television. “There will be other guests, and I'm not going to avoid any of them. I will talk with all of them.”
EU leaders said they will take stock of Russia's actions at a meeting at the end of June. After the annexation of Crimea, the US and EU imposed assets freezes and travel bans on dozens of Russian and Ukrainian officials. But there has been disagreement among the 28 EU governments over progressing to deeper sanctions hitting sectors of the Russian economy such as energy, arms and financial services, as they would have varying impacts on their domestic economics.
Washington has at times appeared frustrated by this disunity, and Mr Obama said that if they did have to move to sectoral sanctions, “it's important to take individual countries' sensitivities in mind and make sure that everybody is ponying up.”
He also said he had “concerns” about France's decision to go ahead with the sale of two Mistral helicopter carriers to Russia, a contract worth over €1.2bn.
“I have expressed some concerns... about continuing significant defence deals with Russia at a time when they have violated basic international law and the territorial and sovereignty of their neighbours,” he said. “I think it would have been preferable to press the pause button. President Hollande so far has made a different position.”
The issue may come up at a dinner French President Francois Hollande was due to host for Mr Obama in Paris. That dinner will take place at a restaurant overlooking the Champs-Elysees, before the French leader rushes back to his residence for a late-night snack with Mr Putin. Mr Hollande is trying to play the role of ice-breaker, and wants to orchestrate a symbolic meeting between the Russian President and Mr Poroshenko, who will be inaugurated on Saturday.