This updated report from David Hughes, political correspondent at the Press Association  David Cameron interrupted his Easter holiday to discuss the crisis in Ukraine in a sign of the growing concern about the actions of pro-Russian forces in the country.  The Prime Minister, who is in Lanzarote with his family, spoke to William Hague by telephone ahead of a meeting of European Union foreign ministers.  The pair discussed the "deteriorating situation in Ukraine" and Mr Cameron said the UK will "press for a firm and united response" from the EU, No 10 said on Twitter.  Pro-Russian forces showed little sign of complying with a deadline set by the administration in Kiev to withdraw from occupied government buildings in eastern Ukraine.  Moscow has denied it is behind the co-ordinated operation by gangs wearing uniforms without insignia, but Britain said Russia would be assumed to be complicit unless it condemned the actions.  Foreign Secretary Mr Hague said it was "vital" that the EU signalled Russia had a responsibility to stop "undermining" Ukraine.  The EU has warned that Russia faces more stringent economic sanctions if it further destabilises the situation in neighbouring Ukraine.  At an emergency meeting of the United Nations Security Council, the UK's ambassador, Sir Mark Lyall Grant, warned of a "dangerous escalation of an already dangerous situation" about which the UK is "gravely concerned".  Satellite images show between 35,000 and 40,000 Russian troops in the vicinity of the border with Ukraine, along with combat aircraft, tanks and artillery, in addition to the 25,000 Russian troops already illegally in Crimea, he said.  While the Kremlin denied it was behind the attacks in eastern Ukraine, Sir Mark said the events "point clearly to Russia once again interfering directly in the internal affairs of Ukraine using manufactured pretexts and military force", calling recent events in eastern cities "a well-orchestrated campaign designed to destabilise the country".  Urging Russia to back down and air its grievances through dialogue, Sir Mark said: "Russia's aggressive stance is a clear threat to the sovereignty, independence and territorial integrity of Ukraine.  "The United Kingdom calls on Russia to immediately redeploy its troops away from the border, to cease all activity designed to heighten tensions and sow discord, and to revoke the mandate given by the Federation Council on 1 March to use military force on Ukrainian soil."  There has been recent unrest in the east of the country, including Donetsk, where ethnic Russians fear they will suffer at the hands of the West-facing Ukrainian government.  Ukraine's interim president, Oleksandr Turchynov, has announced he is sending in the army to resist attacks, stop Russian forces moving in and prevent a repeat of the situation in Crimea, which was annexed by Moscow following a hastily-arranged referendum.  Russian ambassador Vitaly Churkin denied Moscow was to blame for the violence, instead accusing Ukraine of using radical neo-Nazi forces to destabilise its eastern region.  But US ambassador Samantha Power accused Russian of "spreading fiction", saying: "These are not protests, these are professional military operations."
Pro-Russian separatists have ignored a demand from Ukrainian acting president Oleksander Turchinov to disarm and withdraw from Slaviansk