Ukraine was today braced for the possibility of further violence, after bloody clashes between demonstrators and security forces on the streets of capital Kiev left dozens of people dead.
British Government ministers and EU officials left no doubt that they held the regime of embattled president Viktor Yanukovych responsible for the spiralling violence, urging him to pull back police and troops, amid claims that government forces used sniper rifles to pick off protesters.
The EU was drawing up a list of Yanukovych allies who will be subjected to sanctions, including a visa ban and asset freeze, agreed in an emergency Brussels meeting yesterday.
David Cameron was continuing a round of talks with fellow world leaders, meeting Dutch Prime Minister Mark Rutte to discuss the crisis, after speaking by phone with Russian President Vladimir Putin, German Chancellor Angela Merkel and the Prime Minister of Ukraine's western neighbour Poland, Donald Tusk.
Yesterday saw the bloodiest clashes in Kiev since anti-government demonstrations kicked off three months ago after Mr Yanukovych shelved an association agreement with the EU in favour of closer ties with Russia. Moscow then announced a multi-billion pound bailout for Ukraine, whose economy is in tatters.
Unconfirmed reports from local medics suggested that at least 70 died and as many as 500 more were injured as marksmen shot demonstrators, amid chaotic scenes which saw Kiev's Maidan Square transformed into a battlefield, with firebombs hurled at police lines.
The White House said the US was outraged by scenes of Ukrainian security forces firing automatic guns on protesters and urged Mr Yanukovych to withdraw forces immediately from central Kiev.
No American sanctions were announced, but a spokesman said President Barack Obama was considering the options open to him.
The Foreign Office has updated its travel advice for Ukraine to advise against all but essential travel to Kiev. UK nationals currently visiting or living in Kiev are advised to stay inside.
Downing Street said Mr Cameron was seeking to build support for a roadmap for a peaceful resolution proposed by European foreign ministers who held talks with both sides in Kiev yesterday.
Following his phone conversation with Mr Putin, Number 10 said that Mr Cameron and the Russian president had agreed that they should both "encourage all sides in Ukraine to get behind this emerging plan as a way to end the violence and open the way to a lasting peaceful solution".
But Russia's foreign minister, Sergey Lavrov, accused the West of applying "double standards" in the conflict, telling a press conference in Baghdad: "The opposition cannot or does not wish to distance itself from extremist groups.
"Our Western partners and everyone in Europe and the US put all the blame on the government of Ukraine and they do not condemn as they should the actions of the extremists. We are very troubled by all that, because the double standards are obvious here."
Downing Street said Mr Cameron and Mrs Merkel were both "extremely concerned by the spiralling violence" and agreed that President Yanukovych had "a particular responsibility to help de-escalate the situation by pulling back government forces".
The PM and Mr Tusk agreed that the 28-nation EU should "continue to look at the ways it can promote a peaceful and democratic settlement in Ukraine, recognising that continued violence will make it harder to reassure all Ukrainians that their legitimate aspirations will be realised", said Number 10.
A spokesman said that all three leaders gave their backing to the EU foreign ministers' roadmap.
Ukraine is set to dominate Mr Cameron's talks with Mr Rutte in a dinner-time meeting during the Dutch PM's visit to the UK, which will also focus on plans to strengthen the EU internal market, as well as the upcoming European Parliament elections and the appointment of new presidents of the European Commission and European Council later this year.
Foreign Secretary William Hague, who attended the emergency meeting in Brussels, said the EU sanctions would send a "strong signal" of the unacceptability of the actions of those responsible for the bloodshed on the streets of Kiev.
"It should be unacceptable in any city or country in the world, unacceptable in a European city, a European country," he said.
"And it's a signal of the EU's determination to do something about that."
Mr Hague added: "There is widespread horror in the European Union as well as in the United Kingdom at the scale of the loss of innocent life and the events of the last 48 hours.
"Of course we call on all involved to turn away from violence, but some people are responsible for the violence and so we have decided to introduce targeted measures and targeted sanctions involving visa bans and asset freezes on those individuals who are responsible."
Earlier, the Ukrainian ambassador to London, Volodymyr Khandogiy, was summoned to the Foreign Office for the second time in as many days to be told that the action to crush the protests was "unacceptable".