PM warns of possible sanctions for Russia over Syria '˜atrocities'

The Prime Minister’s comments came after European leaders met outgoing US president Barack Obama for talks in Berlin amid concerns about his successor Donald Trump’s attitude to Moscow and commitment to the Nato alliance.

Mrs May said the leaders of the US, UK, Germany, France, Italy and Spain were united in condemnation of the “atrocities” in Aleppo, where Bashar Assad’s Syrian forces are being aided by Moscow in attacks on rebel-held areas.

She spoke of the need to “keep up the pressure on Russia”, including the possibility of sanctions “on those who breach international humanitarian law”.

The Prime Minister also used the meeting to reaffirm her commitment to beginning the formal Brexit process by the end of March next year.

She said: “I want to see this as a smooth process, an orderly process, working towards a solution that is in the interests of both the UK but also in the interests of our European partners too.”

Her statement came as the Supreme Court ruled that Scottish and Welsh will be allowed to intervene in the legal battle over the triggering of Article 50.

It also followed warnings from Germany’s finance minister Wolfgang Schauble that the UK faces paying into the EU for more than a decade after it quits the bloc.

On his farewell visit to the continent, Mr Obama “urged his European counterparts to continue seeking solutions to common challenges with the incoming US administration on the basis of the core values that define the United States and Europe as open democracies”, the White House said.

The Prime Minister said she would update Mrs Merkel on the Brexit process - even though the German chancellor said it was not on the agenda.

Mrs Merkel said : “We will not discuss any further today the British wish to leave the (European) Union.

“That will not be on the agenda because the Prime Minister has already assured us at the very latest that Britain will invoke Article 50 by the end of March.”

She said the Germans would wait until the motion had been tabled for further talks.