Britain on Wednesday accused Russia of fomenting unrest in eastern Ukraine with "a torrent of disinformation" and called on Moscow to lean on pro-Russian separatists to end their conflict with government forces.
In some of its strongest comments on the subject yet, the British Foreign Office said it was not credible for Russia to deny responsibility for events in eastern Ukraine.
"We call upon Russia to use its influence to put an end to the instability. Russia has refused to condemn the illegal actions of armed groups that look to it for direction," the British Foreign Office said in a statement.
"We have heard a torrent of disinformation and inflammatory statements [from Russia] that fuel unrest and create unfounded fears. We have seen a military build-up and maneuvers on Ukraine's borders designed to intimidate."
Britain said Russia's annexation of Crimea had left Moscow isolated on the world stage. London had no wish to isolate Russia, the Foreign Office said, but it and others could not ignore attacks upon Ukraine's sovereignty.
Britain's intervention coincided with Ukrainian government forces pressing ahead with an offensive against pro-Russian separatists in eastern Ukraine.
British Prime Minister David Cameron will hold rare face-to-face talks with Russian President Vladimir Putin on Thursday in France at which he will urge Putin to help de-escalate the situation in Ukraine.
The meeting, which Cameron requested, was originally scheduled for Friday but was brought forward by a day for technical reasons. Both men will be in France for the 70th anniversary of the World War II D-Day landings in Normandy.
It will be the first time the two have met since Prince Charles sparked a diplomatic spat by likening Putin to Adolf Hitler.
British officials have said Cameron wants to use the meeting to encourage Putin to begin to build a working relationship with Ukraine's President-elect Petro Poroshenko.