With the interim Ukrainian government’s 48-hour ultimatum to pro-Russian forces to leave official buildings they have occupied in eastern cities ticking down, the prospect of force being used and an inevitable escalation in the crisis is coming closer.

On Wednesday US Deputy Secretary of State for Europe, addressing a meeting of the Helsinki Commission in Washington, asserted the occupations were well-planned and co-ordinated and involved outsiders, although Victoria Nuland did not offer any evidence in public.

The Kharkiv occupation has been ended, but the barricades still stand in Donetsk and Luhansk, and Russia has warned the use of force could spark civil war.

Secretary of State John Kerry was again on the phone to the Russian Foreign Minister Sergei Lavrov on Wednesday ahead of talks next week that will bring America and Russia round the table with the EU and Ukraine to try and negotiate a path forward, although Nuland is not optimistic.

“I have to say that we don’t have high expectations for these talks, but we do believe it is very important to keep that diplomatic door open,” she told the Commission.

Kerry is pressing along similar lines to Russia’s President Vladimir Putin for a national dialogue to be established between west and east Ukraine to ease the tension, while Putin is continuing to insist on a new federal constitution giving the mainly pro-Russian east greater autonomy.