David Cameron has given Vladimir Putin a "very clear and firm set of messages" during face-to-face talks about the Ukraine crisis.
The Prime Minister told the Russian president the current situation with his troops in Crimea was unacceptable and the pressure being placed on the Ukraine was also unacceptable.
Yesterday's hastily-arranged meeting at Charles de Gaulle airport in Paris happened after the leaders of the group of seven leading industrialised nations warned that Russia could face damaging economic sanctions unless it changed course.
Mr Cameron said: "This was a meeting with a very clear and firm set of messages, which is that there is an opportunity for a successful, peaceful and stable Ukraine, especially now there's been a presidential election.
"But the status quo, the situation today, is not acceptable."
Earlier, at a joint news conference with US president Barack Obama following the G7 meeting in Brussels, Mr Cameron said Moscow needed to recognise the election of new Ukrainian president Petro Poroshenko, stop the flow of arms across the border and cease support for pro-Russian separatist groups.
Russia, which had been due to host a G8 summit in Sochi, was effectively expelled from the group it has been part of for almost two decades following its annexation of Crimea.
Instead the G7 held a summit in the Belgian capital. Mr Cameron then flew from Brussels to Paris for his meeting with Mr Putin, which aides said was a chance to "look him in the eye" and stress the need for de-escalation.
After the hour-long discussion the Prime Minister said: "Russia needs to properly recognise and work with this new president, we need de-escalation, we need to stop arms crossing the border, but if that happens, there is a diplomatic path that is open to have proper relations between Ukraine and Russia and a successful future for the people of Ukraine, which is what they deserve."
In Brussels, Mr Cameron indicated that Mr Putin had one month to end Russia's destabilisation of the Ukraine or face crippling economic sanctions.
"If these things don't happen, then sanctions will follow," he said. "The next month will be vital in judging if President Putin has taken these steps."
Mr Obama, who will also be in France for the 70th anniversary events of the D-Day landings today, urged Mr Putin to "seize the opportunity" opened up by Mr Poroshenko's election in last month's presidential poll to negotiate a diplomatic resolution.
"Mr Putin has a chance to get back into a lane of international law. He has a president in Poroshenko who he can negotiate directly with," he said.
"It's clear that he recognises that Ukraine needs to have a good relationship with Russia, but also rightly affirms the right of Ukraine to engage with the rest of the world."
Mr Obama also echoed Mr Cameron in warning that the western powers could not afford to allow the situation to "drift" and Mr Putin needed to move quickly to show he was serious about finding a peaceful solution.
"The mere fact that some of the Russian soldiers have moved back off the border and that Russia is now destabilising Ukraine through surrogates rather than overtly and explicitly does not mean that we can afford three months or four months or six months of continued violence and conflict in eastern Ukraine," he said.
"We will have a chance to see what Mr Putin does over the next two, three, four weeks, and if he remains on the current course, we've already indicated the kinds of actions we're prepared to take."
Mr Obama expressed his concern over French president Francois Hollande's decision to go ahead with a £1billion deal to supply two Mistral class helicopter assault ships to Russia.
"I have some concerns - and I don't think I'm alone - about continuing significant defence deals with Russia when they have violated the territorial integrity of their neighbours," he said.