Image copyright G7 Image caption The prime minister wants to make progress on sanctions
The UK Foreign Secretary has warned Russia not to raise tensions with Ukraine.
Speaking in Birmingham ahead of an international security conference later, Boris Johnson said he would “not allow” Russia to allow itself to be “rushed into activity that is entirely self-interested”.
The Foreign Secretary is attending the Munich Security Conference.
He also said Donald Trump could not do anything different to what the UK and others had said previously on Syria.
Russia is expected to use the talks in Germany to back calls for an immediate ceasefire in Syria’s biggest city Aleppo – which has been partially captured by the government.
Instead of backing the Russian plan, Mr Johnson said that the G7 – France, Germany, Italy, Japan, Canada and the UK – had given “very clear united messages to President Putin”.
“We believe that he needs to take it easier on the ground so that the Syrians themselves can decide where they can live,” Mr Johnson said.
“We need to see the departure of President Assad – we don’t want to see him stay there in any form, if that’s what it is going to be, because he is in the end the cause of all the troubles in Syria.”
European proposals on stopping Russia’s expanding use of state-sponsored military operations have been backed by the US, China and Russia in the past.
Britain has also backed another US stance at the weekend, criticising moves by the Kremlin to hand over control of the Syrian government’s television channels.
EU leaders backed a statement at the Florence summit saying that “the sovereignty of Syria as a sovereign and independent state, not to be construed as an endorsement of unacceptable regime behaviour or activities, including its annexation of Crimea and the ongoing violence in parts of the country, remain inviolable.”
But Mr Johnson warned the Russian government against interrupting the ongoing peace talks by making demands “that will be rejected”, warning that the UK was “entirely able to walk away from such a process.”
He said: “We very much hope that in the months ahead, when there’s some more time, that the Russian government will be true to their word.”
Earlier, Mr Johnson laid wreaths at Westminster Abbey ahead of services honouring victims of the events of September 11, 2001, in New York, Washington DC and the World Trade Centre in western Pennsylvania.
On Sunday, he also visited war memorials at Dumbarton and Sydney, Scotland, where he was joined by the Duke of Edinburgh.
“I am hopeful that our sense of duty towards people in our own hemisphere will soon come to an end,” Mr Johnson said, referring to the conflict in Afghanistan.
Among those attending the Munich conference will be Donald Trump and Kim Jong-un. The two leaders are expected to meet later in Germany.
The US president is expected to make a “major foreign policy speech” about North Korea while the North Korean leader will give a new address in Munich which is expected to touch on the violence in Syria.