That would include the key opposition demand for early presidential elections, something Yanukovych has shown no sign of conceding since the trouble erupted in November. They spoke of "possible signs of progress" after seeing the president. But Thursday's escalation occurred within hours of Yanukovych calling a truce in the dangerous spiral of violence that is also spreading beyond Kiev, splitting the country east to west, and raising fears of Ukrainian meltdown. The White House said Joe Biden, the vice-president, spoke to Viktor Yanukovych on Thursday by telephone and warned him that the US was preparing to sanction officials responsible for the violence. While the authorities blocked trains coming to Kiev from the anti-Yanukovych west, protesters in the east lay down on railway tracks to prevent the government transporting military reinforcements to the capital. Crimea, ardently pro-Russian if part of Ukraine, issued threats of secession should the country go into freefall. Reports from the west spoke of protesters ransacking military and police headquarters and seizing weapons, while the security services were said to be shredding documents in scenes that recalled the anti-communist revolutions of 1989 in Romania or East Germany. But the authorities were willing to hit back hard by bringing in the army. "Military servants of the armed forces might be used in anti-terrorist operations on the territory of Ukraine," a defence ministry statement warned. The security service announced national "anti-terror" operations, revealing that the authorities were struggling to maintain their grip. "In many regions of the country, municipal buildings, offices of the interior ministry, state security and the prosecutor general, army units and arms depots are being seized," said Oleksandr Yakimenko, the head of the state security service. The mayor of Kiev, Volodymyr Makeyenko, a Yanukovych appointment, announced he was quitting the president's political party. "The events happening in the Ukrainian capital are a tragedy. I have decided to resign from the Party of the Regions." Ten Yanukovych MPs broke ranks and demanded mediation in the spiralling conflict by the EU and the US.